demo
space cadet
I've always used the additional PCI-e power connectors, but there is an additional 4 Molex type connector which was since connected and made no difference.
That molex is the supplemental pcie power.. High end boards often have a 6-pin to the mobo instead of a molex too.
If you don't plug it in you can damage the board, usually with burn marks on the 24 pin socket. If it's already damaged then no, plugging it in afterwards wont make a difference.
That's probably not the issue though, just throwing it out there because you mentioned you weren't using it before.