Need help fixing very slow computer.?

I have a 4 1/2 yr old dell computer & it runs slow & downloads slow. i have deleted files cleaned out the cookies have done a system restore & have done disk clean up & defragment. but it still runs slow & downloads slow. i have the fastest internet speed but with my computer you wouldnt know it. i download music & download video games. but it takes forever and i also have the pogo games site. and everytime i go there to play games it takes my computer a really long time for it to open the game & play. it also gets stuck sometimes when i play the games. my husband says that we need a new computer because of the games that i play our computer is not equipped to handle them. is he right? i hope there is some kind of free program or software that i can download to fix prob. i cant afford a new computer. also if I need to buy a new 1 can i just by a new tower would that be cheaper or can i take tower to computer store and see if they can fix it. email add is tammie24fan@yahoo.com