There are lots of threads on troubleshooting, and a nice sticky on steps to take to resolve. (see Troubleshooting your Tivo, its a bit aged but most problems start and stop with the hard drive)
For you, I would suggest first putting in the original drive and see if that fixes things. You can also run a detailed scan for the upgraded drive on your PC to see if it has problems. Other suspects are a cablecard that may need to be reseated or the power supply.