iMac screen froze while in use, shutdown, restarted, got worse iMac (approx 7-8 yrs old)

Screen froze while in use. Shut down for 10 mins. Restarted, graphics came on distorted. Apple logo in the middle of screen with small broken lines and specks all over the screen.  It tried to load but froze up again. Had to push power button a few times and hold it down to shut off.
Sounds like a dead graphics card. If it's really that old you'll be out of luck to get a replacement card from Apple. Ask a local service provider to be sure.

If you want to rule out software, try booting from an external drive. RAM would be a small possibility as well.