PSU too weak?

[sirfa60]

I have:
Phenom 2 X2 550BE (overclocking is planned for later)
Scythe ZZ for the CPU
4GB Geil 1333
750GB Caviar Green
LG DVD
Arctic Cooling 550RF (550 Watt PSU)
MSI 785GM-E51 Mainboard
Everything works O.K. until..........
I put in a ATI HD 5750 Graphics Card
Now the machine wont start, not even the startbeep, nothing.
I take out the Graphics card, it starts!

I suspect that the PSU may be too weak, is that possible?
I thought Arctic Cooling make good stuff. 550 Watts should be enough.

Any ideas, anyone?

 

[IRONBATMAN]

Shouldn't be the PSU's problem