No Audio or Metering Suddenly!!! Cubase 5

I purchased Cubase 5 in '09, using Mackie Onyx 1640 as soundcard. It has worked PERFECTLY until 2 days ago. I loaded a friend’s Cubase SX project into Cubase 5 to mix for him, and all hell broke loose. No audio, but there was still metering. I closed the project and went back to my normal C5 projects and still no audio! I checked device setup and saw the ASIO had changed from my Mackie ASIO to Fullplex. I switched it back to Mackie, went to VST connections to make sure my busses were still there and active, but now, no metering or audio using the Mackie ASIO. If I switch it back to Fullplex ASIO, there is metering, but no audio. Mackie ASIO, no anything! I closed C5 and played various WAV/mp3 files using WMP and they played fine. I opened Reason 4 and I get an error message saying there is a problem with my ASIO settings. The device manager says the Mackie sound card is working fine. I am so lost, can anyone help with this problem??

Most likely you lost the connections/routing on the channels.
check the mixer!

check the mixer how? what should i be looking for?

For the coinnections / routing on the channels - as Split said already…

forgive me for not quite understanding… i have already checked the routing under the “vst connections” in cubase. all busses are intact, and routing as well… if you’re saying i should check the routing on the mixer itself, could u elaborate on how i would do that please?

You look in the mixer´s routing view, if the tracks are still connected to the correct busses.

I did that prior to posting here. the busses and routing are still intact.