My sink is stained and will not come clean it is 7 years old.
If your sink is Corian, here are two things to try:
Run a few inches of hot water into the sink, and then add several cups of ordinary laundry bleach, such as Clorox. Let it sit at least half an hour. Swb the sides of the sink every so often, then drain the bleach solution.
Scrub the sink with a Scotch-Brite pad, and Soft-Scrub with Bleach.