Well, if you hear 1 beep, then floopy boot, It seems that your mda/monitor is not working.
No, you can't use a MDA with a VGA monitor without converters... but you can use a ISA 16-bit VGA card.
Some Trident/Cirrus Logic/Acumos/Realtek VGA cards can work on XT 8-bit slot. Just check that the "16...