[garp]

I bought a non-running 1979 Suzuki GS750L. It had been sitting for what looked like a few years at least, although the seller told me it was running last summer (yeah right). The oil had been drained, so I filled it with clean oil. The battery was dead, so I charged it. I put in the charged battery but the starter wouldn't work, just the solenoid clicked. The headlight was also dim and the horn was weak and eventually stopped working, which led me to believe the battery wasn't charged enough. So it is now charging some more. While it was charging I decided to check the compression by pressing my thumb on the spark plug hole and cranked the engine with the kickstart. To my horror there was no pressure. I'm not an expert so I don't know if I'm falsely testing the compression.
Now, is this bike worth working on any further? What's the worst and best case scenarios.
I'd just like to know if I'm wasting my time with this.