I have R5E50 installed, runs great except when the front end seems to lock up at what appears to be random times (watching live tv, watching a recording, sitting idle at the myth menu). When it locks up, if watching a recording, the picture just freezes and never starts again. Also get no reaction from the keyboard.

When this happens, I am still able to remotely log in from another machine on the network, and do things like run top, ls, etc. Also, mythweb works as well, and the backend will still record like it is suppose to.

Machine info:
P4 Prescott 3.2ghz cpu
1gig memory
400gig HD
Nvidia gForce 5200fx video card
2 pvr150 cards.
450w PS

Have you investigates the logs? The wiki has awesome troubleshooting information.

Seems that a little more poking around uncovered the real fix, and that is to remove the wireless USB keyboard and use a wireless ps2 keyboard.

I also had that problem, both USB remote control and USB keyboard would lock up my box, had to switch to remote PS/2 keyboard.