anyone help me was working on the computer then went off its a tower will switch on can hear fan etc will not boot tried to put disc in to see but nothing at all its dead completely will not boot up at all any help or advice wouldbe appreciated thanx

First of all check the usual, is the monitor on, does it have a standby light on(to show it has power going to it) check the lead from the monitor to the PC hasn't come out.
Does the machine show anything at all when it first boots up (POST screen), if it does, this would indicate a software/driver fault, if not then it's more likely to be hardware related.

CPU failure?

Can u get any sound out of it? Music , windows start up sound?

thanks for your quick replies have checked the monitor when i switch on computer it says no input signal the only light thats on is the green one hear the fan the orange one comes on and then seems to be rebooting then goes off and just the fan on no music or sound on it usually when on you can hear it booting no mouse or keyboard nothing

Or Graphics card gone a knacker.

Or maybe PSU, last week I had a power supply with a failure on one rail, which made the PCI-E connectors go dead, but everything else fine.