Computer takes a long time to begin booting

Okay so I've just installed a new graphics card (HD5770) to replace my old GeForce 8500GT and the computer is now acting odd.

When I press the power button, it powers up and then tries to use the DVD (or seemingly, one of the hard drives), resets and tries to use the DVD then resets, about five times. Only then does it start booting normally, at which point the monitor turns on etc.

What could possibly be causing this??

My system specs are

- Windows 7 Pro 64-bit
- 6GB DDR2 800 RAM
- Gigabyte M61-PM-S2 Motherboard
- XFX HD5770 Graphics