Want to Delete Partition But Can't?

We have a HP/Compaq 6510b laptop (actually 2) that are having the same issue. When we boot up the system it will go straight to the black screen where it asks if you want to "Start in Safe Mode" "Safe Mode with Networking" or "From last known good configuration" or "Start Windows Normally". Well no matter which one you choose it will go to the screen where you see the Windows logo and the loading bar but at the same time each time the computer will shut down and go back to the black screen with the "Safe Mode" options. I want to either re-image the computer or re-install windows xp but I want to delete the partition first. Anyway when I go to the setup menu when booting up the machine I set the cd-rom to boot first hopefully bypassing the "Safe Mode" screen but thats not working either. HELP! What should I do???