i had that same problem at one point with my pc. it might need a good Defrag, that fixed my problem.
http://www.iobit.com/iobitsmartdefrag.htmlthis program is called Smart Defrag, it is the best that i have found out there. best part is that it's free, and compatible with all windows OS's. install and do the analysis. there are 3 different lvls of Defrag: (Defrag), (Fast Optimization), (Deep Optimization).
i set mine to "Deep optimization" and my PC ran as if i had just bought it again. I would advise you to set it to Deep Optimizations for best work. then set the auto defrag for once every 2 weeks, for keeping it on a stable run environment. Be ready to leave your pc alone for about 3-4 hours if you do the Deep optimization just to let you know.
the reason my pc did that is because i had my 500 Gig Drive filled to 400 Gigs way past halfway mark, and files were fragmented all over the place causing my Hard Drive to work at its max of 7200 rpm speed and still not seek the files in time to work properly, causing the same problems you had and also blue screens and full system shutdowns. this program really does work some magic, hopefully this will fix your pc as it did mine
good luck
also when i used windows defrag analysis it only found 109 fragmented files, 5 mins later i ran Smart Defrag and it found over 2000. that will give you an idea of how in depth this defrager goes.
