If you can access the computer again, open the Control Panel, double click on the "Display" icon, then click on the "Screen Saver" tab, then click on the "Power" button. Once that opens, set ALL options to "Never" by using the drop down menu. In the "Advanced" tab, use the drop down arrow to select "shut down" in the "When I press the power button" option. On the "Hibernation" tab, UNCHECK the box.

Next, just to make sure the computer isn't having conflicts to slow the computer down, please follow the instructions in the links below. Clean things up a little. It may take a while to finish all the procedures but it should help:

For Windows 2000/XP, ignore the first couple of sentences about checking "resources" and the "Performance" tab in the link below but follow the rest of the procedures including the "Services" links at the bottom.

How To Shut Down Unnecessary Start Up Programs

Because the links for the "Services" are no longer functioning in the link above, use this one:

Services Guide For Windows XP

Next, clean out the junk files:

How To Clean Unwanted Files From The Hard Drive

If you're using Service Pack 2 on Windows XP, tidy up a little with these instructions:

Cleanup After SP2 Installation

After following all the procedures above, run Error Checking/Chkdsk and Defrag to optimize the hard drive:

How To Run 'Error Checking/Chkdsk' On Win2000/XP

Hope this helps.