starts but wont run

i recently replaced the head gasket on my mgf tf. now it starts and runs for about 2 seconds then stops.. the run period remains constant. can anybody provide any information as to where i should start looking...thanks
 

The engine dying in the arse may not have anything to do with the resent head gasket replacement, you need to determine if you are getting fuel when it cuts out, you also need to determine if you re getting spark when it dies and another possibility is a blocked exhaust.

Welcome to the forum. As Cobber has said it probably doesnt relate directly to the head gasket change. More likely to be a loose connection or something such as the immobiliser even.

Can you give us a bit more to go on. F or TF, what year, what you have already checked ?

Have a look at the fuel pump, as I’ve said before, I have never had a problem with mine although I’ve looked at a fair number of posts to have gain an understanding of the range of problems with their failures.
If left dormant for a time they can find waking up problematic & as the pump relies on fuel passing through to keep it lubricated, being off the road for a while won’t help.
If it runs for a few seconds, that infers an ignition system wanting to get on with the job, however once the initial squirt of fuel is gone & the fuel rail pressure drops & it turns into a Norwegian Blue.
Try again & the pump might have enough puff to build pressure for another go.
Others might have further suggestions.
M

Starting and running for 2 seconds looks like alarm ecu is not speaking with engine ecu.
What system do you have Lucas or Pektron?
As asked previously - do you have F or TF and what yearmof production?
Is your fob square with 2 buttons or oval one?
Can you lock and unlock your car with the remote/fob without a problem?