what does one red ring mean?

Solution
An error code will appear on the screen as well, which states what component the 360 thinks is faulty.

E67, E68, E79
These could all have something to do with the hard-drive. Try taking the hard-drive out from the 360 and playing without it. If the error message disappears, then your hard-drive is faulty, and you will need to get a replacement. If the error message still appears, then something else is wrong with your 360, and you will need to send in the 360 for repair.

Any Other Error Message
Any other error message is not user-serviceable. You will need to return your console for repair.

Console Codes

Clear AllGame updates, and the Console Game Cache

1. Go to the System Blade
2. Go to "Memory"
3. Press Y on the Hard-Drive
4. Then push X, X, Left Bumper, Right Bumper, X, X
5. Select yes on the message that appears.

could be a problem with the Hard Drive or the disc reader