[PROBLEM] Black screen and no ssh after prolonged inactivity

[GDIT]

I have two distinct problems which may or may not be related. I have installed the latest Xbian on my RPi, which I want to be able to leave on at all times.

First problem: When the screensaver (dim) activates, moving the mouse or clicking the keyboard causes the screen to go black and stay that way. Neither is able to wake it up and the only solution is to ssh into it and restart the XBMC service.

Second problem: After an even longer period of activity (not sure by how much, but definitely longer), the RPi is unable to be accessed through ssh either. The light on the WiFi adapter flashes as though showing activity, but attempting to ssh inevitably results in a network timeout. The only remedy to this is to forcibly unplug the pi and plug it back, obviously not the most elegant solution.

What can I do fix this issues?