Old Laptop powers unexpectedly off

[speedy-MACHO]

Hey people, I have a old laptop which I sort of fixed: the power plug was loose so I soldered the cable directly to the laptop. It's not an important laptop (Benq Joybook DH2100) so I didn't really stick to the general rules: grounding, don't touch the motherboard, don't short circuit leading to beautiful blue sparks...
Actually it went quite well and it just powered on. Windows XP worked ok in the beginning, but after a few reboots it unpredictably powers off, same for BIOS, same for Windows recovery, same for Ubuntu. Now every time I turn it on, it powers off suddenly between 10 seconds and 5 minutes.
I tried RAM separately, no results, and there appears to be no overheating.
Anyone any ideas?

 

[ib2007]

Have you tried undoing what you did and doing it the right way? see if that fixes the issue.

 

[speedy-MACHO]

Have you tried undoing what you did and doing it the right way? see if that fixes the issue.

Yeah no that won't be undone. The pin inside the plug (on the laptop's side) was loose and it didn't make contact, so I removed the entire contact, beheaded the adapter and soldered it directly to the motherboard. LED's indicate the battery is charging and it can still start without the battery, showing the same symptoms. So I don't think the problem has anything to do with my modification.