Sounds like you have a lot of unwanted data on your computer,
First,
Click, Start>All programs>Accessories>System Tools>Disk cleanup, it should tell you the disk you wish to clean (c:), tick all tabs and press OK, this will clean all uneeded files but not your personal files.
Next,
Click, Start>All Programs>Accessories>System Tools>Disk Defragmenter, click analyze, windows will then tell you if this needs to be done, if so click defragment, it should take about 5-30 mins depending on how much it has to do,
These two programs will do nothig to your personal files so do not worry.
Danny, November 2005