Dell Precision M4300 LCD intermittently goes black

About 3 weeks ago my Dell Precision M4300 LCD(a) went totally black from power up ( no bios screen ) -  nothing.    I plugged my external CRT,  and I was operational with the CRT.   I used the CRT for a couple of days with the LCD(a) laying flat (180 degrees),  so that I could see the CRT.    After about two days,  the LCD(a) screen re-appeared,  so I used it for about a week.   Then,  it went black again.    I replaced the LCD(a), with a new LCD(b), using Dell's M4300 manual instructions.   However,  LCD(b) was also black,  so I went back to using the CRT.    On the same day,   maybe as a result of some sequence,   the new LCD(b) is now operational.     Could this be software related ?     Could this be related to the hardware suspend (i.e.  auto suspend mode when closing the laptop )  ?

Appreciate any info.   Thanks.