System will not boot after videocard installation

Went out and bought a Radeon 4850, stuck it in, wouldn't boot. Turned on for just a split second before turning back off. Thought it was probably the 300 watt power supply so I went out and bought a 650 watt power supply by Antec. Installed that. Same thing. Yes, it's getting juice from a PCI-E power cable, yes, the main graphics bus is set to PCI-E x16 in the BIOS and yes, it's in as far as it can go. Though I thought it felt like something was keeping it from going in all the way. There are no visible obstructions but perhaps that L-shaped face plate is coming in contact with the case metal beneath the motherboard?

The computer boots without the card but still turns on for only a split second if it is in the PCI-E slot.

Thanks in advance.

I think the motherboard is probably fine because it still works when I take the card out. I'm now trying to figure out what not powering on at all is symptomatic of: broken video card or not being plugged in all the way. I'm hoping the former because I'll never be able to make another one fit anyways without modifications (give HPs design team a pat on the back) and I can always just exchange it.

Unfortunately I don't know anyone who has a PCI-E slot, either.