I don't know does it make any sense, but sh*t started happening when i bought a new graphics card (Leadtek A280 LE 64MB Geforce4 Ti4200).
I plugged monitor cable in, and everything wuz OK. But, when I turned the computer off my monitor didn't go standby, but shut down too. I couldn't turn it on till I unplugged the power cable and plugged it back in. It happens some times!!! It didn't before!
And sometimes, when I turn the monitor on, picture is distorted, and it fixes only if I turn it off, and back ON. Monitor is ADI Provista 5PM, and he worked great till now.
Are you able to test the monitor on a different system? The time in which the problems started, may have only been coincidental.