When you open it, sneak a quick peek to try to be able to tell if the drum is spinning. Maybe the main drum drive belt has failed and this creates a condition that makes it cut out. I only mention this possibility because this is the most common thing that fails on dryers and perhaps the easiest to fix. If this is what is wrong then check out:
I always suspect a clogged outlet duct, but you said you checked it. You removed the flex pipe where it connects to the dryer and cleaned it out? Does it blow really hard when you turn it on? Remember, when in doubt call a technician b/c you don't want to go BOOOOM!!!