Nothing on screen, fan running on processor, hard... Same problem as Patatas. Some time ago I

Question

Same problem as Patatas. Some time ago I couldn't get the operating system to load. The machine would fire up but at this stage I did have something on the screen. I thought it was a bad sector on the hard drive so I reformatted and everything was fine for about a month. Now the screen is blank again and when I go into the screen menu it tells me that 'no signal' is being received. I have taken out the graphics card (which has worked perfectly up to now) and tried the on-board graphics port but same message. Have tried another monitor - nothing. Have bought a new hard drive - nothing. Given that the hard drive is firing up I have discounted a faulty PSU (am I right to do so?). There is a second hand K7 VT6 Motherboard for sale on e-bay - would this be a reasonable replacement? Thanks