[nicky lawrence]

I am a self taught player, and whenever I play Rachmaninov's Prelude in C Sharp Minor, my forearms get really tight and painful.

I don't know what I am doing wrong (hand positioning etc..) and would be grateful for any advice/instruction to alleviate the problem.

Thank You

Nicky

[D Minor]

[Gill the Piano]

RELAX! After you've played the note, you might as well relax, as nothing you do then will change things. So you've got the sustained notes that you can relax on and check that everything is loose in your arms. Weight should come from the shoulders, not the wrists, so make sure your actual arms - especially the wrists - are relaxed.
Another thought is the height of your piano stool; your arm should be level with the keyboard, not sloping up or down.
But D Minor is right; have a consultation lesson with a good teacher, and s/he will soon put you right. It's a lot easier to diagnose in the flesh...
Good luck!