You should check for conflicts. Right click My Computer > Properties > Hardware tab > Device Manager button. Look for any conflicts in that. Theyll be noted by yellow exclamation points.
You can run an online PC test somewhere like this
and itll tell you anything that seems wrong.
If all else fails, open up your PC and poke around. My brother had a serious slowdown problem awhile back that we found to be the result of CAT HAIR building up on his heatsink....