Have you checked that its trying to boot from the correct hard drive ?  Mine has done this a few times aswell after updating the bios and it simply reset the boot device order and it was trying to boot from the wrong HD.

Hi Ethaes,

Checkout this article; it should help you with your current problem. Also, there's a link within that article called Alienware Desktops No Post Troubleshooting.

Let me know how it goes.

When the issue was just getting the new video card to work it was giving the no post beeps, but after the BIOS update it only gives the option to either run the system repair, which doesn't work, or boot up normally, which leads to a quick bluescreen before restarting itself. I have my older video card in the machine now.

I've tried switching the boot mode from UEFI to Legacy, which just leads to it saying:

"Reboot and Select proper Boot device
 or Insert Boot Media in selected Boot device and press a key"

The normal setup is boot mode UEFI and SATA Operation RAID. Try that and let us know how it goes.