How to detect Microsoft Windows running?
You can use &H2F interrupt service, using CALL INTERRUPT statement:

	'$INCLUDE: 'QB.BI'
	
	DIM InRegs AS RegType
	DIM OutRegs AS RegType
	
	InRegs.AX = &H160A
	CALL INTERRUPT(&H2F, InRegs, OutRegs)
	
	IF OutRegs.AX = 0 THEN
		'Windows is running.
	ELSE
		'Windows is not running.
	END IF
		

If you use QBASIC 1.1 that does not support CALL INTERRUPT statement, you may use the solution provided at ht7: How to imitate CALL INTERRUPT in QBASIC 1.1?