So I use Science skill on the computer you are supposed to use to blow up the mariposa base. And it says you manage to get an interface scren out of the vats control computer. Then when I click on it, all it says is [Exit System] . I have tried so many times, and I fail. What is the problem

You may need to get a security card first. Steal it off one of the nearby techs and it should give you full access to the system.

Search the body of the scientist that was near the computer...if you have forced your way down, if not you must use pickpocket to steal...the missing keycard. Either way use it on the computer with security codes set to silence self destruct.
(31914-1041-1251514).....5 Minutes to go.

Found the solution to this. I was playing through with a 1 INT character, though my science was at 48%. Still, nothing worked (radio didn't deactivate force fields, Security Card or Science would allow access to the Vats Control Computer, but the only option is to [Exit System]). The solution in this case, use dynamite or a plastic explosive to destroy the Vats Control Computer. You will then get 300 seconds to flee the base. I didn't even fight Lou (Lieutenant).