Android : can't reset adb in eclipse , getting error

I have downloaded eclipse and the android sdk tools. but when I create a new application, no layout file is created! instead I'm getting some errors, among them :

Description Resource Path Location Type The container 'Android Dependencies' references non existing library 'C:\Users\YANIV\workspace\appcompat_v7\bin\appcompat_v7.jar' ffffffffff Build path Build Path Problem

and also im unable to reset the adb (in the ddms perspective) : the error i get is :

[2014-12-13 01:42:53 - DeviceMonitor] Adb connection Error:An existing connection was forcibly closed by the remote host

[2014-12-13 01:42:54 - DeviceMonitor] Connection attempts: 1

what should I do ?