just for the sake of science could you press the windows key (usually a couple left of space bar)
press win + r and type dxdiag in the box then hit enter
I'm curious the stats where it says:
Processor:
??
Memory:
? MB Ram
then go to the display tab at the top of that window
and it should say something like
Chip Type:
Fill in those blanks for me
i may not be able to help you but I'd still like to know, especially since you say it speeds up but only slightly.
Do you think it worked better before but now it's completely messed up or has it seemed to slow down over time.