Hi everyone!

My system:
Asus Maximus IV Extreme-Z
Intel Core i7 2600K
4x4GB Ripjaws X
OCZ Vertex 3 Max Iops for system
Seagate 3TB for storage

Until yesterday I had 2x EVGA GTX580 Hydrocopper 2, then I installed 2x Inno3D GTX 970.
I also changed some cables for a cleaner look.

Now my problem: the PC won't even boot into bios. It gets stuck on Error Code B2 "Legacy option ROM initialization", no ASUS logo, no BIOS, nothing. The monitor only shows something about "Nvidia Geforce GTX 970 BIOS", nothing I can do.

The boot device LED is RED, no idea why, I once got into the mainboard BIOS after switching to BIOS 2, all HDDs were recognized.
I then tried booting from the DVD to install Windows, and it got stuck again on B2.

I tried clearing CMOS, but it didn't work so far. I havent pulled out the battery yet though.
I also tried plugging in a USB stick with the 3603 BIOS (which was installed before), but it didn't do anything.

Any advice? Is my GPU Bios not compatible with the mainboard bios? Is my mainboard bios messed up?

Help please!