Just saw the last post, but here is what I wrote before I saw it . . .
Well, maybe, but if it worked before, it should work now, no? There's a window when you right click on the track box header (where the name of the track is) in the arranger. In that window, it will have, at the top, "record" and "playback". In "record," it should say "Soundblaster" or something close to that.
That's where you select the input. At any rate, I would get a decent sound-card--they're cheap and all over Ebay. You're using the exact setup I started on--12 years ago! Stick with the Music Studio for now, but at your first opportunity go up to Samplitude 11, or Sam ProX, or even better, ProX 3 Suite. The Pro X Suites aint cheap, but the musical possibilities are vast . . . . You absolutely want a different sound card though, ASAP. Get that now, and then the better version(s) of Samplitude. Also, you won't need the mixer, unless you want to use it for monitoring.