Qbasic running on windows7 through DOSbox but not running output graph

hello!
i have been programming using qbasic through the dosbox in my windows 7 32bit. it's been good at the codes so far, correcting errors and fine debugging but somehow when you run the program and the expected output is a graph or a simulation, the graph page just stays black. labels like length and temperature appears on the graph page but that's all. all else stays the same and the system prompts 'press any key to continue' and when you press a key, window shuts down.

any suggestions how i may remedy this one?

thanks a lot