MacBook Pro 2010 black screen after upgrades and replacing thermal pas
I've got a MacBook Pro mid 2010 15in model with a Core i5, which I performed some upgrades on:
Replaced 320GB HDD with a 120GB SSD
Replaced the original 2 x 2GB RAM sticks to 2 x 4GB
I then used the machine for a few days, first with macOS Catalina (the patcher), then elementaryOS Linux.
Today I received the correct T6 Torx to replace the thermal paste, so I did that, however a small dribble of paste landed on the board, which I wiped off with some a dry tissue.
I then tried to start the machine, however it didn't work. Turns out I hadn't seated the keyboard connector properly, so the power button didn't work.
I fixed that, but now there's another problem - when I press the power button, the fans spin but there's no other signs of life apart from the battery indicator on the side and the charging light on the MagSafe connector.
I've tried resetting the NVRAM and SMC, to no help. I tried reverting the machine completely to the original configuration (bar thermal paste of course), which didn't work. I also tried completely tearing down the machine and putting it back together.
After the second teardown, I now get the startup chime, but still a black screen, the backlight isn't on either. I've checked the display cable on the logic board and it's fully home.
I'm at a loss as to what to do now, any help is much appreciated.
The one on the left is the old, original paste, centre is when I cleaned them now, and the right is the new paste. Didn't manage to clean much between the capacitors but considering they were drowned in gunk before I didn't consider it an issue.