Looks like a GRUB error message to me. Not having the GRUB docs on hand at the moment, I'd hazard a guess that, for your box, whatever the "rootdelay=" value is set as default, it's not enough. I'd go looking in the online docs for GRUB to see what the default value for that parameter is and where the parameter is located, then start bumping it up until this problem goes away.

Of course, if this problem is *new* with a pre-existing installation, I'd worry about the drive. Vac out the box to get rid of dust which can cause heat buildup, check to make sure all the fans in the box rotate at full speed, and start being religious about backups of that drive, because it might not be around much longer.