Satellite C855-S5194 wont start, black screen, fan pulses

I've seen many posts and youtube videos on this subject, but not with the specific symptoms mine is having.  I've gone through various troubleshooting steps already so don't bother telling me to do a power reset or whatever its called.  Here's the specifics:  When trying to power on the laptop, the fan tries to start, but then pulses on and off with increasing intensity and then dies down and builds up again. Screen is black, power light is on.  I removed the hard drive and same thing.  Here's the strange part:  There is a 4G RAM in slot A and 2G in slot B.  If I remove the 2G from B and leave 4G in A then I get just a single beep, no fan.  If I take out 4G from A and replace with 2G card, I get the single beep.  This model is supposed to work with only slot A occupied.  If I reverse them, 2G in A and 4G in B I get the same beep.  It's only if 4G is in A and 2G is in B that it at least pulses the fan on and off.  I thought it unlikely that it is the RAM and it's just due to another fault that this strange thing happens.  So I stripped it down to get out the motherboard for inspection.  I found a suspect looking solder joint next to where the battery connects, there is a double-pin solder joint that looked like a cold joint, so I resoldered it and put back together.  It basically still does the same thing except the fan does not pulse as quickly just one pulse about every 10-15 seconds, so it seems I changed something.  Anyway, I'm at the conclusion that I need a motherboard reflow, unless it is the CPU which I wouldn't know how to test.  One other thing I noticed when I took it apart was the CPU appeared to have way too much thermal compuound on it [from what I read] It looks like they just blobbed a whole bunch on top and the heat sink squeezed it out all over.  Just wondering if that may have been the cause of overheating that damaged the motherboard or perhaps both RAM cards?  That RAM symptom seems odd.  I didn't feel like ordering new RAM when it didn't seem likely to be the problem, now I'm second guessing.  So does it seem like motherboard or RAM... or the CPU?
Solved!
Go to Solution.

PROBLEM SOLVED!
OK, so the motherboard reflow didn't work.
I found another motherboard online for $130 and that worked.
I think I'm going to get a cooling pad now in case overheating was the problem. 

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