Here is the situation: I have a Radeon 5770 that takes several tries before it starts. I have to turn the computer on and off repeatedly, and maybe one time in ten or twenty, it will start normally and function normally indefinitely (at least for a day or two, haven't tried longer). The remaining times, the computer appears to act normally, but the screen remains blank and the monitor sleeping. The same thing happens when trying to wake the computer from sleep. The computer works fine otherwise, it beeps when booting, and I can even restart it by pressing Alt+F4, R, Enter. Plays the sounds and everything. The problem is the same with two different motherboards (Intel DP43TF and DG45ID). One of the motherboards has on-board graphics, and those work fine every time.
So I'm 99% certain that it is a video card problem. The other 1% could be a power supply problem that's specific to the PCI-E connector, although I did try the two PCI-E connectors that the PSU has, and even an adapter for the hard disk/optical drive/fan connectors to PCI-E connector. And everything else works fine, so it's very unlikely.
What's strange is that, when it starts, it works great. Has anyone seen a problem like this? Any idea if it's repairable?
Oh, and the video card fan and light (it has a blue light for looks) turn on every time, not only when the video works.
I had a similar problem in my Sapphire Radeon HD5770, not as dramatic and severe as yours, though. My problem was happening one time after every ten-twelve cold bootups only. I replaced my graphics card with MSI Radeon HD6850. I no longer experience the problem. All other components remain the same in my computer, including my Antec 650 Watts Neo Power blue PSU.
EDIT: My exact gfx card designation is MSI R6850 Cyclone OC/PE
I have a Sapphire Radeon HD5770 too, the Vapor-X edition. I've been using the card for a couple of years without trouble, and the PSU is a Corsair HX620 (620 W). It can handle the load, so the only possibility would be a PSU malfuntion, but I doubt it. It's more likely the part of the graphics card that manages power.
The problems started a few days ago. I was using the computer for routine stuff like surfing the web, nothing strenuous, when everything froze. I restarted a few times and the screen always remained blank. I immediately suspected the motherboard (I've had several of them fail over the years) so I replaced it with a spare one that I had from a previous fail, but the issue remained.
I'll take it to a repair shop one of these days, maybe it's an easy fix. Else I'll have to buy a new card, 'cause the integrated graphics just won't do.