E153FP stuck in power save mode - Help!

I have a problem with my E153FP - it is stuck in power save mode and I don't know what to do.  I've disconnected the blue VGA cable and run the self test, checked the pins and checked all the connections (all fine) as per the troubleshooting pages.  However, as soon as I reconnect the blue cable, the power indicator on the monitor goes from green to amber and I'm back in power save mode.

 

Monitor is connected to a Dimension 4600 and all was fine until a couple of days ago!

 

Any ideas how to fix this?

 

Thanks