Two common suggestions:
1. Reset network connections. This is under Settings > General > Reset.
2. Perform a full restore on your Touch.
I've had mine about a week and it died on me pretty quickly. I went to the Apple store and got a new sensor which did NOT help, so if a new sensor doesn't fix the issue, it's not a sensor issue (so a 3rd wouldn't fix it).
Mine is working again now; honestly I don't know what fixed it. I did both above things and NEITHER helped. I tried a couple more times to link, reboot iPod, reset stuff some more...and suddenly it worked. So I don't know exactly what fixed it. If you haven't tried the above steps, though, give them a try - I know they work for some people.