okay sounds fairly decent, then the only things I would check is that you have a decent amount of space free on your C drive (less than 50% of your drive free space is good)
second check would be to check that your memory has not failed (check by right clicking my computer/properties)
you may have downloaded a malicious program that is slowing up your computer, very easily done as well, worth running your anti-virus.
maybe you have a lot of programs running in the backround on auto?