Mouse Movement Not Smooth

Dimension 4550/ Win XP
P 4 at 2.4 GHz
1 GB DDR SDRAM
128 MB DDR ATI Radeon 9700 TX
80 Gig Hard Drive
Liteon DVD-ROM LTD136
HL-DT-ST-CD-RW GCE 8400B
Turtle Beach Santa Cruz DSP
Altec Lansing 745 Speakers
P992 FD Trinitron 19 inch monitor                                                                                                                        My PC recently crashed and I needed to reformat the hard drive. That's not the problem. Now I notice that when dragging a window with my mouse or scrolling down with the wheel to read text, there is a jerking motion. Before everything crashed, it was a very smooth movement. Can anyone please help? I've played with all the settings and it's driving me nuts!                   Thanks.