here a few suggestions for what it is worth (actually it is free

)
1. have you installed new or updated DRIVERS?
2. We had a similar problem but I think the line when she drew was zig-zag. Turned out it was the metal screws used to hang the SB. If all else fails (cause I know it it DRASTIC to take the board down, but may need plastic washers over the metal screws. I am not a SB tech so ask a tecki first, I just know this was a problem on one of our teacher boards.
good luck! let us know if you get this resolved.