Hey guys, just installed my first game from GOG, "Star Wars: Dark Forces", and I figures I'll take my chances and play on hard level. The thing is, I don't take any damage. My shields are topped, I've got 4 lives, and I started punching myriads of enemies because they don't seem to be able to do any damage. But it takes away from the experience, I just figured how to set up the controls, and I want to feel the blood pumping through my veins!

Can anyone help?

That's a really weird issue. There are several cheat codes, including one for invincibility, but I guess it is very unlikely to accidently type in "LAIMLAME" without noticing.
Maybe try changing the cycle rate in DOSBox, by pressing Ctrl+F11 to cycle down or Ctrl+F12 to cycle up (basically slowing or speeding up the emulation). Press either combination several times and see if it changes anything.

My guess is the same as Syrion: that it's a CPU cycles issue. You can cycle down in DOSBox with Ctrl+F11, like he said, or open up your .conf file, find the [cpu] section and set cycles=40000 or so (40,000 is roughly equivalent to a fast 486, I think).

I didn't read this until today, but I remember this being an issue for me the first time I played Dark Forces back in the late 90's. I was impervious to blaster fire, but any type of damage that bypassed my shields (e.g. Ree-Yees' punches, falling) did hurt or kill me as intended. I wasn't aware of any cheat codes back then, so I still don't know what caused it. When I reinstalled the game a few years later, it worked normally. I haven't played the game in many years, so I wouldn't know if it's still a problem.

Check settings. Make sure the "Super Shield" isn't on.