POWERS ON THEN SHUTS OFF AFTER A FEW SECONDS. i CAN TURN BACK ON IF i WAIT FOR A MINUTE OR SO, BUT IT ONLY STAYS ON FOR A FEW SECONDS AND THEN SHUTS OFF AGAIN.

This has what's called an Output Offset problem.
Needs to be seen by a professional

Samsung HLN507W turns on for about one minute then shuts off, three blinking lights stay on in front. It is not the lamp, nor the blue lamp cover switch for sure. I unplug it and immediately turn it on. It always does the same thing: comes on for 1 minute, then powers down - there is no wait time in between unplugging and powering on. All fans seem to work and I cleaned the dust out of it. Help.

what kind of tv is it, plasma, projection, lcd??

You can try a master reset which your provider will be able to provide the steps to you on how to do it, or the manufacturer's website. if a reset doesn't fix it than you need to get a new phone through your replacement options for this is a device issue.

Try blowing the dust off mother board. Remove back. Unplug first. Then post problem again

Take the left side panel off and check the CPU fan for dust build-up.
You can use some canned/compressed air to clean it. Be careful not to knock off any components. You can also re-seat the RAM/ memory sticks while you are in there. Good luck!

solder issue at the flyback. try resoldering the flyback

somone with some sort of tv knowledge told me that sometimes people dont realize t but moisture builds up inside and it needs to be dried back out

try removing one neck board at a time and see if it stays on and longer,don;t let the board touch any metal or a short wil follow and you got problems.try the red first,