The flashing light gives hope that the problem might be related to the CD/DVD drive (cheap and easy to fix), rather than to the hard drive (major disaster).
Open the CD/DVD drawer manually by opening up a paper clip and pushing it in the little hole:
https://tinyurl.com/yb9bylc6
If there's a disk in there, remove it. Close the drawer and try to boot the computer again.
If that doesn't work, and you're confident with a screwdriver, open up the PC, unplug the CD/DVD drive and try again.
(I'm assuming that you've not got anything like a memory stick plugged into a USB drive, or a media card inserted into a card reader. If you have, make sure that you remove them before trying to boot the computer)