What's your hardware?
Does it work when nothing is connected to the card/breakout box/whatever is hooked up to it? If it does, then the connecting device has too high a load.
Can you get 5V output using MAX's test panels? If it does, the vi is the issue, and you can post it.
If it's an E-series DAQ card, you can run the online diagnostics to see if your card is at fault:
http://www.ni.com/support/selftest/
2006 Ultimate LabVIEW G-eek.