Bad news. The Zen V Plus is known for screen problems - early warning signs include screen discoloration, lines on the screen or dimming. Eventually, the screen will go black.
Possible reasons include poorly-mounted screens, short life of OLED displays, and susceptibility of screens to damage from moisture.
Best bet for a replacement screen is buying a scrapped Zen V Plus on eBay. Here's a great guide to taking apart your Zen.
Disassembly of Zen Plus