See if there are any Diagnostic Trouble Codes stored in the computer... turn the ignition switch on-off-on three times within five seconds and then leave it in the on position. Give the diagnostics time to run, any stored codes will eventually display in the odometer. If you did it right and gave it enough time to work, 4-5 seconds is normally enough, you will always at least see the '55' code which simply means no more codes follow.
If you get any codes, post them up here and we'll help if we can. Could be anything from a bad Crankshaft Position Sensor to a bad fuel pump.