Windows 7. I have tried the 30 secs/ 1 min button trick to no avail. Just before "death" the screen split in two halves (left side on right side) with the mouse working after a fashion on both. Changed monitor to no avail. There is no run down when switching off as before, just off.
Any further ideas?
My first reaction to this would be to think that your graphics card is faulty. If this is a desktop machine, then this is easy to check - just swap in another one. If this doesnt work then perhaps a motherboard issue.
If this is a laptop then Im afraid it will need to go to a repair shop to replace the parts - unless you are confident in your abilities to replace the inner workings.
With it instantly powering down, it seems the machine is not getting past the initial "Power On Self Test" (POST). This can be caused by a bad graphics card, but is more often motherboard trouble.
You dont mention any beeps coming from the machine. This could be because no internal speaker is attached, or that it doesnt even get this far in the POST but could help with diagnosis if you just havent mentioned them (how many beeps? is it a repeating pattern of beeps? ...).
For this next bit ensure you take proper anti-static measures (and photographs if possible).
It might be worth removing everything from the motherboard that isnt needed. This will discount anything else that might interfere with boot. What you need is the processor and fan (make sure the fan is turning), at least one stick of memory, the power supply, a graphics card, a monitor, and the power button connections. If you do remove them make sure you make a note so you know where to put them back. If it boots now (you will get an error message on the monitor to say there are things missing), then replace the things one at a time until you find the one that causes the machine to not boot.
I have tried firing it up without the graphics card, monitor and 1 Memory card and get 1 long and 2 short beeps. The monitor is from the predecessor (this one in use at the mo with the original monitor). I think we can discount the monitor possibility. When I put it all back together with graphics and full memory,without the monitor, there are no beeps. Each time it shuts down quickly.
I will start looking at the options for replacement over the week-end.