thermal problem

in missions,and in free flight thermals are visualised,but the glider gets zero lift
it used to work,installed on second drive under xp plus install add ons one at a
time and testing, it works fine.but i use xp for other things so its temporary.
i cant reinstall or repair on my first drive which is where i want it,because i
dont want the hassle of getting my sdk back working.this has got to be a guage or effects file thats been corrupted or overwritten.any ideas of where to look?.fsx,pack1 and 2.fsx acceleration,vista home prem.jim