CPU usage is 100 %

I am using windows 7 ultimate and it was all going good till I tried to copy music files from a Portable Player through usb to my computer and i used "Show Hidden Files and Folders" to view audio files as I didn't see any of them then there was a System Folder and I tried to open it and BANG my Pc got stuck and Problem of 100 percent cpu usage appeared for the first time!! I shut down and restarted and scanned pc with nod32 and malware bytes to no avail!! CPU and Memory usage is still higher than normal!! Thanks in advance for your help!!

Welcome

Few things to try.

Type memory diagnotics, in search and take the test.

Type event viewer in search and look for errors.

When the cpu spikes type process explorer in search, download and see what is using the resources. You may want to download it now to be ready.

Try clean boot and try to
see what is using the memory
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7

Agreed, try other solutions in the troubleshooting guide in my sig too. I would also add more RAM, 2GB isn't sufficient anymore.