My van wont start now ?

I haVE JUST REPLACED MY THERMOSTATIC HOUSING ON MY VAUXHALL ASTRA VAN AND THERE WAS A NOISE COMING OUT OF MY WATER CAP I GOT A NEW ONE AND SINCE GOING ON MOTORWAY THE WATER LIGHT CAME ON SO STOPPED ON HARD SHOULDER AND THERE WERE LOADS OF WATER NEAR THE PASSENGER SIDE UNDERNEATH...I TOPPED BACK UP WITH WATER GOT HOME AND NOW MY VAN WONT START ???
DOES ANYBODY HAVE ANY SUGGESTIONS FOR ME ? tHANKYOU