Why does my Tivo Series2 work fine, then after 10 mins it freezes?

I have Tivo Series2 tcd540040 and it works perfectly fine, but after 10 mins of watching live tv it freezes up and makes a scrambling type picture, it reboots eventually, then repeats cycle, 10 mins it freezes up and scrambles.....it used to work fine for 2 years.....is this a sign of a dead hard drive or something else?