Hello,
I have exactly the same problem, but it is a Samsung SyncMaster T220HD. Says "Check Signal Cable", when there's nothing wrong with the cable. I also have an ATI Radeon, and I use Windows 7 Ultimate 32.
"Check signal cable" is a generic error message. Could mean the video card has gone or it could be a fault in the signal processing circuitry on the monitor.
Choices: borrow another monitor to test you computer or test your monitor on a friend's computer.