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.