The standard check with suspect displays is to try them on a different computer, which eliminates any possibility of the fault being at the computer end - have you tried this?
You should also check the connectors at both ends of the cable, it's surprisingly easy for a TFT display cable connector to become loose at the monitor end.
If you do all that and the display is still not right, take it straight back to the supplier and ask for a repair or a replacement. Don't accept any excuses, but understand that most suppliers can't repair monitors themselves, they send them back to the makers. The supplier is liable for the repair under the sale of goods act, but in any case you have a 3 year manufacturer's warranty on the monitor in addition to your rights under consumer law.