Wierd Aircraft lighting

Wondering if anyone else has had this occur in FS2K. Just recently whenever the A/C lighting is on, they appear as large "square" blocks of colored lights where the position lights etc. should be on the A/C. Also the wave action, dust and engine smoke are all rendered in "Blocks". This does not happen in any of the other flights sims and I have made just about every adjustment and tweak I can think of just short of doing a new installation of the sim. This had occured once before and I can't remember what corrected it or if it just dissapeared! Any input would be greatly appreciated.Bewildered,Easyflyer