iv had the same problem with my old systemax PC. there are many ways to increase performance speed on a computer. here are just a few i recommend to you that should work:
1 defrag your hardrive (C)
2 delete any unecessary files/apps that you never use
3 download freeware to clean your computer (ex-CCleaner, ATF Cleaner, etc.) these basic programs remove temporary internet files/cookies and clean your registry. these usually take up anywhere from 500-1,000 MB of memory on my laptop.
4 OR, if all else fails, you could perform a system restore to an earlier date when your computer wasnt as slow. and i think it gives you an option to restore your PC to its original factory settings for a fresh start. but if you run a system restore, remember to save all your useful files/images/music/etc. to a data-sufficient flashdrive BEFORE restoring.
hope this helps and good luck!