Perhaps you have never burnt your Recovery DVD's? (2 DVD's that take you back to Factory Restore) you can only do this once as then the option disappears on HP slimline.
Disconnect from the Internet and close all other software.
Creating recovery discs is a resource-intensive process.
Click Start , and then All Programs .
Click PC Help & Tools and then Recovery Disc Creation to start the program.
A Welcome screen opens.
Agree with robinofloxley, that's what I do. I then have the option of 'Back to Factory' - or with an image of my C:\, back to 'up and working in half an hour' with no configuring/tweaking/reinstalling programs I've added, to do. Personal Data I keep on a separate harddrive anyway and also back that up/copy it separately.