Strange MAV on Vista

You could try a program such as:

print "hello world"

If that doesn't run, that's bad.
Maybe the 2D modes can be set?

graphics 800, 600, 0, 2
setbuffer backbuffer()

text 0, 0, "tested!"
flip
waitkey
end

And I would advise to only test one thing at the time. Combining all tests into a big program could give distorted testresults. You could however create a batch file that runs several testprograms after each other.
Anyway, I would try this program:

Print "starting logfile"
ff = writefile("log.txt")

test = 0

For b = 1 To 4
bt = 8 * b

print "testing " + b*8+ "-bit modes"

For w = 0 To 2048
For h = 0 To 2048
	If GfxModeExists(w, h, bt) Then 
            s$ = w + " x " + h + " x " + bt + " ...... tested OK"
            writeline ff, s$
            test = 1
        End If
Next
Next

Next
If test = 0 WriteLine ff, "no graphics modes found :/"
WriteLine ff, "final test started"
CloseFile ff

Print "log file is created."
Print
Print "now one final test"
Print "to see if mode"
Print "1680x1050x32x1"
Print "can be set"
Print
Print "press any key to continue"
FlushKeys()
WaitKey()
FlushKeys()

Graphics3D 1680, 1050, 32, 1

camera=CreateCamera()

light=CreateLight()
RotateEntity light,90,0,0

; Create cube
cube=CreateCube()

PositionEntity cube,0,0,5

ff = OpenFile("log.txt")
WriteLine ff, "mode 1680x1050x32x1 was tested succesfully"
CloseFile ff

While Not KeyDown( 1 )
TurnEntity cube,0.1,0.1,0.1
RenderWorld
Text 0, 0, "if you see a spinning cube, the final test has passed successfully"
Text 0, 20, "press esc to end"
Flip
Wend

End

I used it once in a similair situation and it turned out that there were NO graphics modes that could be found.
If every test fails, and this customer isn't fed up, you could consider using BMax+MiniB3D. If you need a test program for that, here:
link to yousendit
It is your original test program, ported to minib3d.