Blank screen on Power ON

[nix_88]

Hello,
My system's configuration:
Intel DP45SG motherboard
Intel Core 2 Quad Q8400 processor
Transcend DDR3 4GB RAM
ATX Cabinet with 500W SMPS

I purchased this system 2 weeks ago and got it assembled from a local hardware dealer in Mumbai,India.
During the first week when I presed Power ON, the LEd's and the fans came ON but the screen used to be blank.Then on turning it OFF and attemoting to turn the computer ON,the system used to finally boot and work OK on the 3rd or 4th attempt on the Power switch.
And the now the problem is bigger.
The computer refuses to boot and the screen remainsblank even after several attemps to turn it ON(earlier 3 or 4 attempts used t be enough)
All parts are newly purchased and are unlikely to be defectve.
The RAM seems to be OK.
The screen has been tested and it is not a display issue.
Please help me trubleshoot this roblem.
I spent a lot of money on this system and need to make it work!

 

[o1die]

I would start with the power supply. I had a cheap unit fail in only 4 days. Most that come with cases aren't very reliable. One exception is the ps with antec cases.

 

[nix_88]

I would start with the power supply. I had a cheap unit fail in only 4 days. Most that come with cases aren't very reliable. One exception is the ps with antec cases.

Thanks a lot Oldie.
I did try changing the power supply and my system started working.Earlier it didn't even turn ON! BUT
now I'm facing other issues!
My computer keeps restarting on its own.
Even when left idle the system restarts after some 2-3 hours and on playing videos it restarts after about 30-40 minutes.
Although I have heard automatic restarts are a sign that the system doesn't have enough power,I have tried running the system on a whole bunch of power supplies ranging from 500W to 750W.
I have just installed a 750W SMPS and my computer restarted even on his one!
I really don' know what I can try now.(since I have already tried 4-5 different power supplies )