Which TiVo model is it?
Have you tried removing all external devices? (wired ethernet, wireless ethernet adapter, phone line, CableCards, external storage, antenna coax, cable coax, etc.) Basically, start it up with just the power cord attached and with no CableCards installed. I know that some TiVos wouldn't reboot completely with the wireless adapter connected during the GSOD.
Your hard drive might either be bad or the contents of the drive have been corrupted. Or you could be the victim of the capacitor plague, meaning your power supply has bad capacitors in it. This could have caused the corruption of the hard drive.
If you are willing to do some tinkering, you could open up the TiVo and test the hard drive using a manufacturer's test CD in a PC. Most of the time, the hard drive will test perfectly, meaning the software is corrupted and must be replaced. Sometimes, you will get a bunch of S.M.A.R.T. errors or bad blocks detected, meaning the hard drive is about to fail. If it is clicking, you are seeing the drive in its death throws and it must be replaced as soon as possible.
While you have the TiVo open, look at the capacitors on the power supply. If you see any bulging or leaking, you have bad capacitors. The easiest thing to do is to get a replacement power supply, but this can be expensive. Or you could use a soldering iron and replace the bad capacitors with the same capacitance values.
Depending on the model of TiVo, I can help you with getting clean software images. Let me know via PM if you need an image.
Hope this helps,
1+ Pioneer DVR-810H-S
1+ Pioneer DVR-57H
1+ Toshiba RS-TX20
1+ Humax DRT400
1 Humax DRT800
Most with Lifetime and upgraded drives
All Series 2s with Linksys USB200M