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I bought a Sapphire Radeon HD 5770 video card, but am having problems getting things running smoothly. I'm certain it's seated correctly and I do have the 6-pin power connector attached.

When I turn on the computer, the fans and lights turn on, but it takes ~1 minute to post. It typically freezes at the "TAB=Post, DEL=Setup..." screen. Oddly enough, though, there have been a few times I have been able to get booted all the way into Windows 7, and even try out some games.

I first thought the problem might be with my PSU. It just barely exceeds the minimum requirements (req=450W, mine=480W). I don't want to buy a new PSU on a hunch though, especially considering the fact I got into Windows a couple times.

I'm an experienced computer user, and have done my share of research before posting, so I'd prefer to hear from someone who has seen or heard of this kind of behavior before, and has a potential fix.

Update 7/25

After some more fiddling, I confirmed that the PCIe slot is fine (old card still works). I reset the BIOS to fail-safe defaults (+ enabled the LAN ports). It has been booting up consistently, and I haven't had any problems gaming. It still takes about a minute for the computer to POST, compared to only a second with my old card.

I'm thinking the problem is either my PSU (likely) or my motherboard, although it's booting up now, so I won't mess with anything until I buy a new PSU in the near future.

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Running a PSU that close to the minimum may well lead to problems. That card can draw quite a bit of power. I'm actually surprised that you didn't mention a crash while gaming.

But booting and installing an OS are times when the machine's hardware and PSU are under the greatest stress. It is not unusual during those times for the CPU to be at 100% for an extended period. A borderline PSU will start to show problems.

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