You will need to eliminate the various things to sort out what is going wrong.
I noticed you say no digital picture, does this mean the analogue tuner is working? If so does your TV use a loop-through cable from the analogue to digital tuner like Sony TVs do?
If you have access to a second TV to hook up to the antenna would tell you if the antenna is the problem. Also changing the antenna cable from wall socket to TV is a good idea. If the antenna is a problem a company like Kaz Electronics can help.
http://www.kazelectronics.com.au/ If a second TV works OK then its checking the TV. Make sure its connected correctly. A few years ago I accidently connected the antenna cable to the antenna out on a new LG TV. I spent 10 minutes wondering why its reception was so poor until I noticed my mistake.
Although this is rare I believe that some equipment can be tripped up when auto tuning by the fact that all channels use the same numbers from both Black Mountain and Tugg Hill - the equipment will lock onto the weaker Black Mountain channels and ignore Tugg Hill. Check that the channels are tuned into the following frequencies:
SBS UHF 57 Hor 732.5 MHz
ABC UHF 59 Hor 746.625 MHz
SC10 UHF 62 Hor 767.5 MHz
WIN UHF 65 Hor 788.5 MHz
PRIME UHF 68 Hor 809.5 MHz