MacBook Pro shuts down when opened

This has just randomly started happening this evening.

Whn I close the lid for my MBP, everything happens as normal, but then when I open it, sometimes the login screen will appear for a brief moment or two then close as if when the lid is open, the computer behaves as if it has just been clsed.

Am genuinly concerned and have tried like he brightness buttons but they don't seem to help. Sometimes it will work for maybe 7-10 seconds but doesn't fully properly work.

Nothing like this has happned before and am quite worried.

Please help,

Thanks,

Micah