Hi Pino68 - I remember your name, but don't remember what the trouble was. Glad it worked up to this point... hopefully we'll get it working again
Let's focus on there not being any signal shown on the meters, when using a Microphone that is connected directly to the D8B. That should always work, no matter what's going on with the computer you have connected (once we get a Mic working, we can move on to making sure the audio interface works again).
Just to make sure you're looking at the right thing: Is the correct layer selected? (push Mic/Line button for channels 1-24).
Is the mic connected directly to the XLR input on the channel you want to test? Is the "Mic" button pushed for that channel (channels 1-12 only!). Is the gain up? If the mic needs phantom power, is that turned on? Did you try a different Mic cable, already?
If all of that looked right, but you still don't see any signal on the input, I'd first try if the Startup session might have gotten corrupted (or accidentally changed) and messed up your routing.
To do this, I'd move the file called "Startup" out of the Session 5 folder on the Mackie harddrive, then restart the D8B. It should create a new Startup file with the default routing.
After the re-start, try again if you get signal from the Mic inputs on the D8B.
(There are more details in the database, how to make sure the D8B doesn't find another Startup song from elsewhere, like the root of the harddrive, etc. Check the "Corrupt Session Files" section in the database, here:
http://www.sonido-7.com/d8b/maintenance.html)
With the Startup file "hidden" or deleted, the Mic input level should definitely show something, if all the settings were made as mentioned above. If that's not the case, then something might have gone bad.
I'll let others chime in, but in that case, I'd probably try re-seating the BFC and 25-pin cables that go to the rack unit, first (with the D8B off).
If that doesn't help, I'd probably try to reseat the ribbon cables on the inside of the D8B next (and maybe use some Deoxit on the contacts while you're at it).
...but let's do all of this one-by-one. Again, I'd try to hide (or delete) the Startup session first, and check again if you get signal from the Mic input after rebooting the D8B.
Best of luck!