I installed all the components of my new computer and powered up. Everything looked good in the BIOS - everything was detected. I opened the DVD tray and put in the Vista DVD and then closed it. Vista started loading, etc... and then I powered off the box because I noticed one of my fans wasn't blowing.
I fixed the fan and powered back up... now the DVD tray won't open. All I did was lay the case down to access the fan and power cycled. BIOS continues to detect the DVD drive but the tray won't open again.
There should be a small pinhole in the front of your DVD drive. If you straighten a paperclip and insert it there, it should physically operate the mechanism sufficiently for you to get the drive door open and recover your DVD. Depending on why the door wouldn't open, it may work after this, or may continue having problems. If the latter, replace the drive.
If the parerclip dont work your disk probably fell out inside the drive while you had it on its side, causing a jam. I've seen it happen before. If this is the case you will have to dismantle the drive to get the disk out.