Did it do this eversince with this particular mining setup or onl since an update to BFG or the miners?
My first guess would be a problem regarding the drivers or windows handling so many USB devices.
Try setting the display options of BFG to be more verbose and enable logging so that BFg tells ou more about what's going on that could help you get to the ground of it.
never worked right with windows so I moved to ubuntu - it was okay for a little while but I wanted to consolidate it with my scrypt rig so now I have this version of bfgminer running in the background - everything boots up and runs fine for maybe 40-70 minutes then it dies off. doesnt give a communication error or driver error it just says pool stratum pool requests work update