How much to repair my BenQ FP22W 22" lcd?

Its normally okay, but sometimes (rarely, like once every 3 months or something) the lcd will switch from dvi to d-sub display input for no reason and switch back again non stop. Need to turn it off n not use it for a day or so only it'll become normal again.

No splitter, DVI slot.

Nope, the monitor will switch between the dvi n vga signal but it wont stay put, it'll just keep on switching between the 2 inputs until I turn it off.

Since I only use the DVI signal, so when I turn on the monitor, it'll be like this

Turn on -> DVI display as normal -> VGA display suddenly appears (which means no display, since the VGA isnt connnected) -> DVI display -> VGA display -> DVI display -> VGA display and so on, and so on until I turn it off.