I replaced the motherboard on a Toshiba L355D-S7901. When plugged, in the power light and light signifying it was on were lit green. The fan would run, but all I got was a black screen. I replaced the motherboard and got the same thing. The only difference is that after reseating memory, changing memory, or even reseating some of the various plug in cables, on occassion suddenly I would start it and get the BIOS screen. I went ahead and set the time and date and when I went to save the changes lost the screen. It did not go black tho, you could see a backlight until I shut it down and restarted it would be a black screen again. Reseat some things once again, and got the bios screen and again the same thing happened. All this time the CPU fan ran, I could feel some heat from the vent although not abnormally hot. I am at a loss. Not sure what else to try. I have used different memory, tried with the hard drive removed, with the dvd drive removed, with both removed, the battery in and the battery out. Someone have any suggestions? I have repaired numerous desktop computers, but am somewhat new to laptops other than replacing screens.