|Assuming that the computer is clean you could try some TLC|
1) Uninstall any old / unused applications as they can add bloat to your computer, slowing it down.
2) Perform a disk-clean on the computer
CCLEANER is a good program to help remove the clutter that builds up over the years.
3) Perform a disk defragmentation
Start -> All Programs -> Accesories -> System tools -> Disk Defragmenter
This will help organize the files on your hard disk so that the computer can load more efficiantly.