In trying to re-install WindowsXP it recycles me to a window that tells me to start up windows in SAFE MODE, SAFE MODE W/COMMAND PROMPT, LAST KNOWN GOOD CONFIG., AND START NORMALLY. I have tried each of these and cannot enter them, just get recycled back to that page. I have powere down and it still brings me back to that page when I power up. How cn I now wipe things clean and start over?