NEC Projector VT440

Question

Used every day in our school. Recently had new bulb and has had polariser replaced in the past. Image is fading, adjustments to colour, etc. makes no difference. Video is Ok-ish but image from computer is terrible, very faint and white background is blue-ish. Any ideas that won't cost a lot?! We have to decide now between spending more money (we've had this one about four years) or buying a new one.