Hi @dirktooth,
Since you have reseated the cable (both ends - presumably not damaged or connectors corroded - did the tablet get wet or was it dropped at all?) between the systemboard and the display assembly unfortunately as a DIY repair the way to prove whether the problem is in the screen or the systemboard is to temporarily replace the screen and check the result.
No audio is also a problem but until you can “see” you don’t know what is happening in regards to the audio.
It may be a systemboard problem affecting both video and audio or it may be two separate problems. If you think that it has turned on did you try increasing/decreasing the Volume to see if an audio is there when touching keys etc?
Replacement screens are available online. Just search for Galaxy Tab 2 10.1 LCD screen to get results for suppliers.