My theft light is flashing and my 1999 F-150 won't start. I checked the fuses and relays to see if one was burned out. I tried disconnecting the battery to reset the computer but to no avail. If someone else has had this problem and solved it please let me know how you did it so I can try it myself. Thanks

 

You should have a second key. If so , try the other key.
The keys are coded to a particular vehicle. Depending on your reply will wait.

 

I tried that whit no results, I think that the fuel pump rely is not working.That is my next pursuit. Thanks

 

This might help some,
The flashing anti-theft light is telling you something is not right and it starts with the keys possibly contributing to the problem. There are other requirements that need to be checked out and a scan tool may be required.
The security system sensing something is not right will not allow the fuel system to operate.
A problem like this is not something someone without the tools and knowledge can usually correct. Even if you manage to somehow get the fuel pump to run the injectors still will not work until the underlying problem is corrected.