I had the exact same problem with my 6 month old machine. I had recorded an episode of The Simpsons and selecting it in the program library froze my machine. There is no way to format the machine like a PC so I returned it today for a replacement.
Only problem with this machine is the remote isn't very responsive, ie. takes a few presses of any button to get the desired effect. Had the exact same problem with the machine I just took back for its last couple of days. My firmware version is 2.81.
By the way I've never had more than 70 hours of available space, how can Thomson claim its got 120 hours
EDIT: Left the system on standby while watching 300 (awesome film), it updated to firmware 2.91
The remote still feels unresponsive. The red LED that lights up when you press a button doesn't light up every time, so even simple tasks are frustrating 
I will give it a couple of days to fix itself but if it doesn't I'm trading it in for another brand.