|If it works okay on a different PC, there is nothing wrong with the monitor iteself.|
Try a new signal cable. if that doesn't help then your computer's graphic card may be faulty. if it's a PCI or PCI-e graphics card (ie not integrated with the motherboard), carefully remove it and then firmly push it back into the slot.
Before touching any internal components, unplug the PC from the mains, then discharge static electricity from your body by touching the bare metal chassis of the PC. Now it is safe to touch internal components.