Major Display Problem

Earlier today I was playing Far Cry, when my computer crashed partway through loading a level. I reset it, and when it started up again there were several vertical lines going down the display. These persisted throughout the boot process, until the point where Windows normally started. At this point the monitor came up with an error...

OUT OF FREQUENCY
HF: 120 KHz
VF: 150 Hz

...and stayed that way until I reset the computer again.

I then tried restarting into safe mode, which worked fine; although the vertical lines were present on booting, they disappeared when Windows started up. I reinstalled my graphics drivers (nVidia 56.72), but that had no effect at all. I also tried switching the monitor for another CRT - again no change, except the new one just turned off (presumably because it wasn't designed to display status messages).

My system:
Time Computers 19in CRT monitor, model 778Si (2.5 years old)
A64 3400+ (2 months old)
MSI K8N Neo Platinum (2 months old)
1024Mb Corsair 3200XL RAM (2 months old)
MSI Geforce 5700 Ultra (6 months old)

So my questions are:
What exactly went wrong?
More importantly, how can I fix it?

Thanks in advance for any help