VDU wont display anymore

Hey, i have a really old Tiny desktop with windows 98, about 2 months ago i decided to reformat it, i did pretty well and the monitor was displaying fine, i then left it alone for about a month (exams), but now i have come back to finish reformatting it only to find the vdu won't display anymore when i plug the vga in, the light on the vdu turns amber but when i take it out or plug it into my laptop it turns green and displays. Any ideas?

Thanks