My computer has been working fine until this morning when it froze shortly after logging into Windows (mouse/keyboard unresponsive and frozen display etc). I switched the computer off and on again, and from this point my monitor has been displaying a 'no signal' message when the machine is powered on. I've tried running it without external/usb devices and the same thing happens. All lights inside and outside the machine are behaving normally as are fans. All cables are in properly (cable into back of monitor was loose but the problem persisted after tightening it). The computer doesnt beep when turned on, but as far as I recall it never did anyway. My graphics card (gts250) is only a year old and never overheats, and has plenty of power. Unfortunately I have no spare components to swap in to test.
Any suggestions? I've just started a new uni course so this couldn't have come at a worse time. Any advice extremely gratefully received,