HELP with giant spiders and Indiana Jones boulder

[Hekai]

I am using Windows 7, 32 bit and it is a desktop.

I am in the spider cave where you take the round boulder, put it in the organic acidic slime, hope over, turn right and see a bridge (three planks).

As I near the bridge the very large boulder behind me dislodges and chases after me (Indian Jones and Raiders of the Lost Arc style).

As I approach the bridge, whether holding the shift key or not, I walk and hesitate, so much so that just as I clear the bridge I get squashed. I have tried breaking the bridge, jumping in the pit and jumping out. Sometimes I get it but it seems I wind up in the wall and have to play from the water cave (last saved game). When I am "in the wall" I can see the glow stick and pick axe but the background is all a taupe brown and I cannot move anywhere. This is definitely a glitch.

I have read online experiences of other games and have watched some videos where people just RUN. It is smooth as well as quick (at this stage neither is true for me). Other people say they clear the bridge and smash it-I have time to turn before being crushed.

I don't think it is my computer or processor as the game has run smoothly and well up to this point. I tried to uninstall and reinstall the game once. There didn't seem to be any issue while installing it. I am confused and frustrated. Thanks.