Radeon 4770 - Underpowered PSU

On a similar subject, I've just bought a Radeon HD 4770, which requires a 450W PSU, which I thought I had but turns out that it's only 400w (and not a very good one either).

The computer will POST, make it to the Windows XP screen then cuts out (everything is still powered but won't make it to the Welcome screen) - am I safe to assume that I just require a new 450+W PSU?

I was using a GeForce 8800GT beforehand, which has just recently went pop hence the new purchase.

Haven't a clue how many amps - didn't try getting into safe mode, just took it out in case I was doing any damage and system restored.

I uninstalled all the Nvidia drivers previous to the ATI installation.

Only reason I suggest going into safe mode was to see if it was a resolution issue with the monitor. So once it gets past the Windows XP loading, the screen goes blank but everything keeps running?

More correctly, the screen powers down - from the LED power-on button being static 'on' to flashing 'off'.

the 8800GT uses more energy than the 4770 so I don't think it's a PSU issue.

As I say, I've rolled back the PC to pre-install of the 4770 and it's running fine again.

Only running XP - and not a GT, sorry, a GTS.

I'll give it a go now and get back to you...

Well I tried all that, and still no luck.

Set resolution to 800x600, restarted in safe mode, worked ok but wouldn't let me change resolution at all and, when restarting in normal mode, still wouldn't get past the Windows screen.

Update:

Still no success.

Replaced the PSU as I thought my 400w cheapo pre-installed one could have been the problem. OCZ 600W Stealth (good reviews for the price, mostly a Zalman apparently!) and still exactly the same - gets to the Windows loading screen, then monitor switches off before it gets to the Welcome page.

Tried in another PC and works fine.

The mobo is a Gigabyte GA-73PVM-S2, which switches off the on-board graphics from BIOS, so I can't think that's the problem.

Only odd thing, when I'm running on on-board graphics it can see my Samsung SyncMaster 204BW monitor - when I switch over to the 4770 it only sees Deafult Monitor.

I'm pretty sure the problem is there somewhere along the line, but I've tried reinstalling the monitor driver before installing the GPU drivers and it won't let me - won't recognise the GPU is installed until I put the drivers in and, when I install the drivers, that's when the problems arise.

Ever wish you'd stuck with what you know? (Nvidia never give me these problems )

UPDATE:

The tech help at Gigabyte has pretty much confirmed that the card is incompatible with the motherboard.

I suggested they could perhaps exchange my mobo for one which works as I can't return it to the dealer due to it not being faulty.

I'm not holding my breath.

I've tried that, mate.

In fact, I've tried everything I could possibly imagine.

I've put the latest drivers on, I've updated to the latest BIOS, I've even tried, in case there were some dodgy drivers I couldn't find which could be conflicting, formatted my drive and clean-installed.

I've bought a new PSU and tried another graphics card (which worked with no problem at all), I've also tried my card in another PC (again, no probs).

Too late to return the 4770? Sounds like you've covered your bases. Sell it on Ebay, recoup what ya can and order a new card...

Gigabyte makes some of the mobos out there. Which board do you have?

The 4850 is a better card, and sells for the same price these days.

This is why you post a full spec list when asking for help. Had I known you had an Nvidia chipset MB we probably would have figured out the problem two weeks earlier.

The issue is not the manufacturer, but a combination of two bad chipsets from Nvidia.

And don't let Gigabyte do that. There is no "Incompatibility List" for GPUs on their website. They need to replace it with a MB that will actually work, like a P43 or P45.