Does the motor spin? If not, then the switch at the top of the clutch pedal or a loose ground wire on the block (heats up from running then stops contact till it cools and contracts till it touches again)
If the motor does spin, either you are getting no fuel (fuel pump relay, pump resistor is cracked or pump is dying) or no spark/injector signal. (weak CPS, melted harness on exhaust manifold, bad coolant sensor for the computer or corrosion between the coil and ignition box under it.