My machine is not booting anymore. It is a debian squeeze server on amd64 with 4 hard disks and 2 software raids (md4 and md5). You can watch this video of the screen after switching it on. (The video says "ubuntu" in the title but it is debian squeeze)
Could this be a hardware issue? Maybe an SATA cable? It happened after moving the box to another location.
Cables should always be checked first.
More info on your raid setup would be helpful, but I'll make a suggestion based on common cases.
Your first disk (first sata) is failing and might cause problems to the rest of the system. Remove it and try again. Depending on your raid setup, you might be able to boot with the rest of them(e.g. if you have setup your / filesystem on raid1).
Booting with a livecd/usb, will help you diagnose and repair/recover lost data.
ata1.00: exception,ata1.00: failed command: READ FPDMA QUEUED,ata1.00: status: { DRDY ERR }. Yes, these are signs of a failed hard disk, or a disconnected cable as forcefsck suggests.