Very Slow Everything

ok....my mums pc had a virus, and after removing that, it was still acting funny, so i went ahead and reformatted...now its still going really slow...hanging at every possible thing when running any program...even the start menu hangs when IE or something is up, so i'm assuming it's hardware related...i was told she had a cheap-ish mainboard and a new CPU installed by a friend of her's, i have no idea what the MB was but the CPU appears to be an Intel Celeron D (3.33 Ghz). i dont know very much about this sort of thing...so if there's any other info i could provide, just ask...thanks.

 

What exactly did you do when you reformatted?
Did you load motherboard and device drivers after installing Windows?
Have you got a load of yellow ?s in Device Manager?
To find full details of your mother's PC you can Google a free download of Everest Home.