Give the following procedure a spin
if it doesn't work then you have to obtain the Dell Recovery CD
Press the F8 key at startup
Choose "Repair Your Computer"
(see the phony progress bar)
Choose keyboard layout
Enter your user name and password (Admin is disabled if you've created a user)
Choose "Dell factory image restore"
Tick box to reformat and restore to factory condition.
PS: The Dell Dimension 4600 came with a recovery cd rather
than a partition. You will need to call Dell and
have them send you a recovery cd and then use that
disc to restore your computer to factory defaultshttp://www.user-guides.co.uk/cddownload/Dell/DellDimension/Dell-Dimension-4600-XP-Driver-CD-Recovery-Restore-Disk-115568.htmlhttp://support.dell.com/support/topics/global.aspx/support/dsn/en/tree?c=us&cs=19&l=en&s=dhs&journalid=CB666653649211DB9D0A359A1778ACFD&treeid=FFA33DA99941FEDFE030030ABD62041A