My Laptop/tattoo seem to be very sensitive when connecting them... and they often refuse to connect until i have power cycled both
so my suggested troubleshooting process would be:
-Uninstall HTC sync
-Reinstall HTC sync (ensure its the most up to date version)
-Power cycle phone
-ensure USB debugging is on
-ensure it is set up to connect to HTC sync (not mobile network or mass storage)
Then connect it and it will install the drivers, if it doesn't connect then, restart the phone and try again.
and if it still doesn't work them i'm all out of ideas!