98 sonoma wont start

i hae a 98 sonoma s10 i got off work today and when i went out to start it it started and shut off immediatley and it never started again and when i try to start it the motor rocks hard and the security light flashes when i turn the key over to the on position it has spark,fuel and is deffinetley in time what could it be any help? thanx.

ok, tried to start it last night and... it will start for and run for 2 sec and then shut off. it keeps doing this...? any sensor gone bad?... cel is not on....