hey theoldras, im only 11, and I've tried my best.
Here are some suggestions:
1. Try getting a different monitor
2. Try cleaning all connections (monitor connections, and so on),
3. Try just cleaning EVERY possible thing inside the PC,
4. Try taking out the cd-rom, card reader (if you have one),
5. And if all of the above does not work try re-installing ubuntu WITH an old monitor plugged in.