dell desk top

[Jim Edes]

this computer has become very slow.

 

[Phillip Corcoran]

Try running the Disk Defragmenter - don't use the computer while that is running:
Start > All Programs > Accessories > System Tools > Disk Defragmenter

Also, do not let the free space on the hard drive get too low.
You need to keep the free space at least around 20% of the drive's capacity.