I had the same problem for many weeks (Delta 1010LT, Win7SP1, Core2Duo). It was working fine before... Searching around it seems we're not alone. Try the instructions here:
- Take the breakout cable off, and reseat it
- Swap the Delta 1010LT into a different PCI slot
- Clean the Delta 1010LT's PCI contacts with a soft bristle toothbrush.
I saw signals on both the left and right channels in the M-Audio Output tab, but the actual signals on the output cables were only on the left (odd-numbered) cable of each stereo pair. Choosing Multichannel output, OUT1+OUT2, OUT3+OUT4 etc. all gave the same results.
BTW, as this question isn't related to programming, it might be better asked on SuperUser.com
Update: The problem eventually resolved for me, weeks later. The cable attached to the breakout cable was found to be broken. Although I had tried switching cables before, to no effect, now replacing the cable worked. At the same time it's likely that all power and cable connections to the PC were unplugged for an hour or so, as the PC was moved. My hypothesis is that the bad cable caused the card or software to end up in a bad state, which simply replacing the cable wouldn't cure: the PC needed to be completely unplugged from everything to clear the problem. It's also possible that moving the PC reset some contacts, e.g. on the PCI or breakout cable.