I'm sorry to hear that you're having this issue.
Without being able to inspect the unit, it's hard to determine. I would recommend having your unit serviced by an authorized technician.
Well I have a Samsung UN46B6000 and I'm having the "famous" clicking sound when I tried to turning on, it takes 2 to 10 minutes to power on the unit...
I was sure that I had power supply problems and the board was replaced... and surprise!! The problem is still there and now I dont know what to think...
What else can cause this problem?