Has the resolution changed?
You also might try updating your driver, even if "you think it probably doesn't need it". Often times, it's the little details that can fix a big problem.
Keep me posted.
After turning the monitor on, the screen turns on momentarily as normal for a seemingly random time - on average a couple of seconds - then the screen suddenly goes blank. This is regardless of which mode the monitor is in, and if the monitor is in TV mode, the sound still works fine. It had been working fine for 6 months beforehand, and I haven't changed any connections etc in that time. Any ideas what could be the problem?