Are monitors only supposed to last 4 years now, or is there something else I can try?
The primary components (lamp, LCD panel) are usually rated for at least 60,000 hours of operation but cheap is as cheap does, and you may have other problems come up such as low-quality soldering or components on the control board. Early RoHS-compliant devices, in particular, can develop problems well ahead of schedule.
You can try scrolling through the ongoing Samsung thread
and see if any of the described repairs might offer guidelines for troubleshooting your TV's electronics, but otherwise, you may just want to save up your money and buy a higher-quality unit.
He who laughs last, laughs first next time.