The fault is not in the PSU.It is on the main board this was proven by techies who post on the Dell Technicians forum.
Spidy
July 2008
Hi I have just had a look at one of these with the same fault when you put the power on you can hear a relay click and then nothing.
I took out the power supply and had a look at the back with a strong magnifier and found six dry joints I have redone them and the telly works fine hope this is of some help.
andy
June 2008
Automatic Answer
While you wait for answers, we may have found some information which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix televisions.