I suspect that the ONLY attack you can do without a gyro is a "thrash" at infantry in your hex, and I'm not sure if even that is allowed. I seem to recall that weapons fire relied on gyro information, so you couldn't target anything without a functional gyro....which seems a bit odd (it should probably give a penalty to tracking moving targets or something), but I think that was the basic rule. Optional rules relax a lot of the requirements, so you probably CAN fire weapons if you're playing with those optional rules. The various generations of rule books (dating back to the Compendium or earlier) are at home, so I can't look it up here.
Firing torso and one arm's weapons with no legs was allowed, but I seem to remember that 2 gyro hits was considered a "mission kill" and removed from play.