If you have another 12v PSU, 2.5amp or more try changing that first. Otherwise it so going to be cabling or LNB.

In my view, when fault finding, please to avoid ABM/AB 28.2. Manual scan, selecting 28.2 is the surest way to confirm reception. Otherwise check several transponders in signal finder. Don't fall into the trap of checking one transponder and saying everything is fine.