Having had a similar problem and reading a lot around this, there seems to be several things that cause freezing and reboots
1. Cachecard or other NIC (if you have one) not plugged in properly - undo the tabs on the motherboard, lift it up and push the card home on the connector. If you can see any of the gold connections, its not right.
2. Failing PSU - They're cheap (you even get one free with 2 spare remotes - Change it.
3. Stray IR - Remove or switch off all other IR sources in the Tivo Room
4. Failing hard Disk - Should be evident by stuttering and lockups while watching TV.
Did I miss any?
Call me Alan, Fred1 is just a forum name; 120 Gig HD; Cachecard; Mode 0; Tivoweb; EndPad; Dailymail_jazz; Hackman; Slingbox (UK version)