first, try UNPLUGGING the computer, and then press the power button & DVD button a few times.
( Residual power left in the system after recent system changes have been known to cause interference)
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If that doesn't help then you may want to consider ONE OF 2 other OPTIONS.
1.RETURNING THE COMPUTER TO "OUT OF BOX" condition.
Computers have a hidden partition that holds all the files needed to create recovery disks , or to boot into recovery mode.
This returns the PC back to the day it was first logged onto. or "OUT OF BOX " running condition.
See your manual for this.
Certain keys need to be pressed during the boot process.
THIS DESTROYS ALL DATA
2. CREATING A "LIVE" Operating system.
A live operating system runs off of a CD/DVD or A USB flash drive.
"OUTSIDE & SEPARATE" from the hard drive.
.
This will run an operating system outside of, & TOTALLY separate from the hard drive itself.
This allows you to gain access to the installed hard drive without using it's own operating system.
This way you will at least know if your drives/partitions are still in working order and also be able to retrieve any data that is on them.
Then you can transfer that data to an external source, like another hard drive or flash drive.
And once that is done, you can go back & either perform a TOTAL restoration of the originally installed operating system ( the "Out of Box method), OR just format the entire drive & install your favorite operating system.
I have supplied the information about UBUNTU below if you want.
READ FIRST.
http://www.howtogeek.com/howto/windows-vista/use-ubuntu-live-cd-to-backup-files-from-your-dead-windows-computer/
(If the addresses below do not show as hyperlinks, then copy & pate them in your browser)
( HOW-TO)
http://www.ubuntu.com/download/desktop/create-a-usb-stick-on-ubuntu
( 32 & 64 bit)
http://www.ubuntu.com/download/desktop
http://www.ubuntu.com/download/desktop/thank-you?country=US&version=15.10&architecture=amd64
IMPORTANT NOTE:
.
To run the LIVE operating system, You need to set the BIOS to BOOT from the USB drive.
GOOD LUCK