You shouldn't even be running the machine with the back cover off, a very dangerous practice.
Tthe fact they are not glowing doesn't mean they are not working, the only way to test the elements is with a megger or multimeter, WITH THE MAINS PLUG REMOVED.
If the element coils appear to be unbroken then its likely to be OK.
Any of the stats or sensors will stop both elements from working not just one.
The High/Low heat switch can also fail on the odd occasion, not common though.
The condensor should be the first thing you check, it should be cleaned out on a very regular basis, once a week on well used dryers.
That which can be asserted without evidence, can be dismissed without evidence.