So when I open minecraft forge with rubidium, the loading bar doesn't move, and after a few seconds, minecraft says it's not responding, and it's going to stay like that forever, I left my computer running minecraft overnight and it didn't change.

Probably an issue with another mod. When Rubidium updates some mods must be updated too. How to find which one?
M A N U A L L Y___O N E___B Y___O N E (well, at least that's how I did it)
In my case it was SnowRealMagic, yours must be different. P.S: GLHV!
(I should probably mention that this is but a mere speculation and your issue might be of completely unrelated origin)

I think this is not a problem with another mod, because this happens even when I open Minecraft with just Rubidium.

Rubidium just had an update, might be fixed now)

and I discovered the problem, my computer didn't have Java 8 installed

no, i think that the problem is with my computer, but thx for the help