Normally that IS an error code beep for video(one long tone and 2 short). If you have an extra vid card lying around, try that or make sure your current vid card is fully seated.
My gf2 is a pain to seat sometimes. Although it appears to be seated, it's slightly raised on one side and I have to REALLY press to make it go in all the way.
Takes yours out and reseat it and see what happens.