Ok, first of all, I'm not sure if this is hardware or software related, but I suspect it may be hardware.
Earlier in the summer, I was doing some programming on my NXT (with leJOS), and everything was working fine. However, when I pulled out my brick to test if it would work with FreeBSD or not, I noticed that when I turned it on, the screen would be filled with lines flashing back and forth in all directions; it was just garbage coming out on the screen. Everything else seems to be working fine. When I press the buttons, it does make the click noise, and if I can blindly navigate through the menu, I am still able to select and run a program.
So my first guess was that the firmware was corrupted. So, I set the device in firmware update mode, and ran nxjflash. The device turned on, but had the same problem.
So after quite a while of Google-ing for a solution, I found that nxjflash has the -f option which will reformat the device in case something does go wrong. So I tried that... still didn't work.
So... I finally got a hold of a Windows computer, which I was able to use to upload the Mindstorms firmware. After downloading the latest update and flashing the device, again, same problem.
I took out my screwdriver and opened up the device to see if anything was loose which might be causing the problem, but could not find anything.
There are fresh batteries in the device.
Does anybody have any suggestions? If I can't get this fixed, I will have to buy another NXT set for a new brick. It has been over one year since I have bought the device, so I can't ask LEGO if they would replace it.