Android : My App wont compile and when it throws an error all my resource files are gone

For some reason whenver I try to compile my android studio project, It keeps saying my image "default" is invalid. It doesn't make any sense because in the XML file it has no issue displaying when you change the view to design mode for the view. After I compile, the Gradle throws an issue and all my "R." turn into Symbol not found. i.e. whever i did like R.id.textview, all my R's turn red and I can't change it back.

My Errors:

Error:error: invalid symbol: 'default'
Error:Execution failed for task ':app:processDebugResources'.
> com.android.ide.common.internal.LoggedErrorException: Failed to run command:
    /Applications/Android Studio.app/sdk/build-tools/android-4.4W/aapt package -f --no-crunch -I /Applications/Android Studio.app/sdk/platforms/android-20/android.jar -M /Users/Anuraag/AndroidStudioProjects/Weather/app/build/intermediates/manifests/debug/AndroidManifest.xml -S /Users/Anuraag/AndroidStudioProjects/Weather/app/build/intermediates/res/debug -A /Users/Anuraag/AndroidStudioProjects/Weather/app/build/intermediates/assets/debug -m -J /Users/Anuraag/AndroidStudioProjects/Weather/app/build/generated/source/r/debug -F /Users/Anuraag/AndroidStudioProjects/Weather/app/build/intermediates/libs/app-debug.ap_ --debug-mode --custom-package com.anuraagy.weather -0 apk
  Error Code:
    1
  Output:
    res/drawable-hdpi-v4/default.png:0: error: invalid symbol: 'default'

Main Activity

package com.anuraagy.weather;

import android.app.Activity;
import android.app.ActionBar;
import android.app.Fragment;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.os.Build;

import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.StatusLine;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

import java.io.ByteArrayOutputStream;
import java.io.IOException;


public class MyActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my);
        if (savedInstanceState == null) {
            getFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment())
                    .commit();
        }
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.my, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_my, container, false);



            RequestTask task = new RequestTask();
            task.execute(new String[]{"http://stackoverflow.com"});

            return rootView;
        }
    }
    public static class RequestTask extends AsyncTask<String, String, String> {

        @Override
        protected String doInBackground(String... uri) {
            HttpClient httpclient = new DefaultHttpClient();
            HttpResponse response;
            String responseString = null;
            try {
                response = httpclient.execute(new HttpGet(uri[0]));
                StatusLine statusLine = response.getStatusLine();
                if(statusLine.getStatusCode() == HttpStatus.SC_OK){
                    ByteArrayOutputStream out = new ByteArrayOutputStream();
                    response.getEntity().writeTo(out);
                    out.close();
                    responseString = out.toString();
                } else{
                    //Closes the connection.
                    response.getEntity().getContent().close();
                    throw new IOException(statusLine.getReasonPhrase());
                }
            } catch (ClientProtocolException e) {
                //TODO Handle problems..
            } catch (IOException e) {
                //TODO Handle problems..
            }

            Log.i("",responseString);
            return responseString;
        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            //Do anything with response..
        }
    }
}

My XML

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MyActivity$PlaceholderFragment">


    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imageView"
        android:src="@drawable/default"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />


    <!--<TextView-->
        <!--android:layout_width="wrap_content"-->
        <!--android:layout_height="wrap_content"-->
        <!--android:textAppearance="?android:attr/textAppearanceLarge"-->
        <!--android:text="80&#xb0;F"-->
        <!--android:id="@+id/textView2"-->
        <!--android:textSize="90sp"-->
        <!--android:layout_alignTop="@+id/imageView"-->
        <!--android:layout_alignRight="@+id/textView3"-->
        <!--android:layout_alignEnd="@+id/textView3" />-->

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="It's definitely sunny. now."
        android:textStyle="bold"
        android:id="@+id/textView3"
        android:textSize="70sp"
        android:layout_above="@+id/textView4"
        android:layout_alignLeft="@+id/textView4"
        android:layout_alignStart="@+id/textView4" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Stop being lazy and just look outside bruh >.>"
        android:textSize="14sp"
        android:textColor="#7f8c8d"
        android:id="@+id/textView4"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />


</RelativeLayout>