Engines won't provide thrust

[Buran CA]

When I activate an engine that I have used before on the same mission it doesn't provide thrust anymore after I have time warped ahead.  If I wait in real time it works, but if I time warp to get to a further point in the mission it looks like is on just no thrust.  In the engines status box the difference is there is no "Fuel Flow", and "Prop. Requirement Met" stay at 0, and the status says off.

Any ideas how to correct this problem?

[sal_vager]

Well, first I'd check to see if I have any of the appropriate fuel, then I'd look here.

Depending on your mods you might be losing fuel to boil-off,