Gear only produces sound when connected to Cubase

I may be tripping, but recently, my studio gear (keyboards, Akai MPC, sound modules) only produce sound when there is a Cubase 5 project open, with an armed audio track(!) For example, I used to be able to make a beat with my MPC and keyboards connected via MIDI, before I even started Cubase. Now, I won’t hear ANY sound from ANY gear unless Cubase is open.

I’m using an M-Audio Profire 610 audio interface and I suspect it might be the culprit… but really not sure.

My speakers are connected to the 1-2 outs on the back of the Profire 610, they are on, and all other cable connections are correct. I recently had to upgrade from Windows XP SP3 32 bit to Windows 7 SP1 64 bit, because my PC had caught a virus and files had to be backed up, and the HDD was reimaged, I believe, before Win 7 was installed. So my computer system has been through alot of changes recently; wondering if this has anything to do with my problem?

Anyone have any experience or ideas as to what is going on here?

Check software mixer/ CP.