Screen is Dead

Hi i have had a iMac G5 for about 4 years now with no problems. Recently the screen refuse's to work when i start it up. This was an intermitent problem but has become pretty much the normal for the last week. We have had builders in for 2 months, Could dust have got into the internals and caused this or is somthing broke ? If i increase the volume i can hear that its booted up i just cannot see anything.

Any Thoughts ?

Try reseting the PRAM and SMU. Resetting the SMU can resolve some computer issues such as not starting up, not displaying video, sleep issues, fan noise issues, and so on.
http://docs.info.apple.com/article.html?artnum=2238
http://docs.info.apple.com/article.html?artnum=301733