Assuming this is 2007 this must be A1226 or A1260.
No no no not a connection issue!! How does it appear to be connection? This is wishful thinking that it is a cheap solution, based on nothing! and it NEVER is!!!
On this model it can equally be a bad 8600M GPU or a bad screen. External monitor is no help because output to external uses different protocol so sometimes it can be fine even when internal does not work.
You can try another LCD to see if it will fix the issue.
Or, if your machine uses the reverse frame LCD, N154C3-L01 or N154C3-L02. Keep in mind these are electrically compatible, but not physically. it will fit but the metal frame will be off. Apple used two different LCDs with different frames just to make life difficult - the only way to tell which yours has is to open the machine or run some command in terminal that escapes me at 4:30 in the morning.
LP154WP4-TLC* and B154PW04 V.3 are ***NOT*** compatible, even though they look similar. People always buy them first because they are cheaper, they go to some old Sony & Compaq and will not fit into your machine without an adapter cable & EDID code reprogramming, which you do not want to &&^& with when replacing your own laptop screen.
Do keep in mind all of these LCDs went out of production seven years ago so everything available now is refurbished trash. Also keep in mind that motherboard is incredibly likely to die for no reason even after you fix it, if you do have the capability to replace the 8600M. Do not reball or reflow it, those are bullshit "fixes" that do not fix anything, almost as dumb as the oven fix.
I would junk this. The frame will break after you replace the LCD on the bottom like all of these do, if it is the LCD now the motherboard will die next week, if it is the motherboard now and you fix it then the LCD will die next week. That's assuming the stock 120 GB Fujitsu hard drive hasn't kicked the bucket already. Ultimately you would be best off just trashing this and moving on.
We shoot arrows through them here. https://www.youtube.com/watch?v=uQix8wqX...