2408WFP goes into Power Save and won't come out

I bought a 2408WFP monitor last December and have had 6 weeks of good service from it. Suddenly, last week, it started to go into Power save mode for no apparent reason and won't come out. I have to restart the computer in order for the monitor to turn on again. I have been in touch with Dell, who won't go any further than the first 5 minutes of my call as they insist on having the Service tag number fo the monitor - even although they sent me an email back in December saying that monitors did not possess a Sevice tag! I have now email customer care but haven't heard back. I am furious at having spent all this money on a monitor which is still under warranty, to have Dell's Technical Support all but wipe it's hands of the problem! Has anyone else had this exact problem with the monitor as yet?