I can barely se the desktop,it is very dark. acer aspire 1710

It sounds like you are or have lost your backlight. In most cases this can be the inverter, it sits under the lcd panel behind the lcd bezel. Unless the unit was dropped or suffered a shock of some kind, I don't think it would be a broken ccfl backlight bulb. Check for loose connections at both ends of the inverter, sometimes these connectios get pulled because they run through the hinges and can get caught or rubbed bare. Below is the link to the service guide that will help in the disassembly. Inverters can be bought on Ebay for under 25 bucks. There is always the chance that this is the ccfl bulb, it is built into the lcd panel itself and therefore it is more cost effective to replace the entire panel then try to disassemble the lcd panel and replace the ccfl bulb. Good luck

http://tim.id.au/laptops/acer/aspire%201710.pdf