A googling tells me the Samsung HC-P4363W is a projection TV. Without googling further, I'm going to assume this TV uses 1 or more projection CRT's to produce the picture. This calls for high voltage (20KV +) which under certain conditions can generate excessive X-rays. To prevent this, TV mfgrs build in high voltage shutdown circuits. The conditions which produce excessive X-rays depend upon several things, one of which is the current drawn by the CRT at any given time. Consequently, the shutdown circuit will commonly be triggered by picture scene content and/or quick change in content. Most shutdown circuits are designed to 'latch' in the shutdown state. Since you indicated you must unplug the set to get it to work again, I suspect the problem is with the high voltage shutdown circuit. It could be something bad in the high voltage circuit or it could be as simple as a misadjusted high voltage control. Regardless, it is beyond the care and feeding the typical end-user can supply and should be left to a qualified technician to repair. But, your mother-in-law might get a few more miles out of it if she turns the brightness and contrast down a bit.