Windows 7: Windows explorer problem

Hi everyone i just joined here and i hope i will get some help.
My PC (everytime that i turn him on) open a little window which says "Windows explorer not responding" then it doesn't ask me if i want to wait till it responds or end the process it just restart it and then its repeat it self....over and over again...i cant open any shortcuts or open anything, right now i am using my computer from Safe mode with networking which i choose after i manually restarted my PC.
I did not installed any software lately and these are they thing i was doing:
Downloaded MP3 file that i opened in itunes
Downloaded MKV file
plugged my iPod to the PC
and tried to record a video from youtube with Bandicam and it gave a message that says it cannot save the video or something i dont remember.

If it helps:
Core 2
2gb ram



I really need help guys i cant listen to music or play Skyrim and it makes me feel lame and noob... luckly i managed to backup my important content before that problem appeared

Welcome to the forum
Try to use the Restore option, then do a scan for virus by the mean of WINDOWS DEFENDER OFFLINE :

What is Windows Defender Offline?
At the bottom of the page, download the appropriate version.
Good luck

Well first of all thanks you for responding.
second thing is what do you mean restore option? and how can i turn windows defender off? thanks you very much again

When did these problems start?