If you can get the DVD drive-door open, put the re-install disk in, then do a "restart" (or just hit the button until it turns off, then hit the button again).
Then, it will boot from CD/DVD--IF you press a button, during the 1st 3 seconds of boot-up......then you can re-install from DVD (if all that was wrong was the operating system wasn't able to use the dvd drivers to run the dvd [and if the dvd mechanical part is still functioning]).