Cintiqs being so expensive it might be worth it to get it repaired by an independent shop (Wacom’s own service if out of warranty would likely be £££ expensive).

Could be just a faulty power port, crimped cable or a blown fuse or capacitor, something that wouldn’t be that hard a fix. Depending on its age, you could also have the CFL backlight tube replaced, the old one is probably quite aged and no longer colour accurate.