Problems with pc

Hi...
My computer for GW can be really slow..you know the occasional lag etc etc
I think my computer might have a problem though...after a month or soo my computer slows down for GW a lot!and i mean a lot, like towns taking extra 30seconds to load or something...not just once but every time...
I usually get so frustrated that I restore my computer(i really have no important files on here like iTunes or work or anything), and the problem is fixed...for like a month...
I know the problem is not the client..i used to reinstall but it would still be slow..whenever i restore its fixed for a month..
I know my computer is good enough for GW because it works great all of the time until this usually happens.I don't think I have a virus or spyware because I do virus and spyware checks like 4x a week...
My pc always starts slowing down at the same time of the month or the month after I restore...does anyone have a reason for this?Please let me know...it'd be really helpful if I can get some help from some of you guys

well, my first advice would be to avoid using system restore, instead...try saving what you want, downloading drivers, and reformatting,...system restore tends to gunk up your computer more than it was before hand and causes lots of problems...it probably even made your problems worse