Boot to your Windows installation disk and follow the prompte to install.  Be sure to delete any partitions shown before installing. That should get you started at least ... if you need more assistance, let us know what OS you are installing.
I have a Dell Optiplex 330 that I am attempting a total wipe and reset. I don't care what I loose, or want to restore at all. I have looked online and tried to find directions for this with no luck. They all refer to having a restore point, and my system keeps telling me it won't do it with no back up point. Can anyone tell me how to do a total system blank and reinstall without having a restore point or back up?  Any help would be appreciated!  
Trying to Totaly Wipe and reinstall my Dell Optiplex 330