Please help me!

Start by removing all the layers of old dye with a colour remover. If you are in america, One& Only Colorfix is available at sallys. You will probably have to do this more than once.
You may not be able to achieve blonde if your hair is very stained, but it should give you a light enough base for colours to show on.

How damaging is the colorfix?

It isn't damaging in itself, it does dry your hair out though which can cause damage to very fragile hair. Much safer and more effective than trying to bleach the colour out. You will end up with an orange patchy mess

Even if I do it twice?

What about color oops?

I am not in America, so we don't have those brands, but from what I have read Colorfix is better than Color oops. Bleaching the colour out is a terrible idea, however many times you do it.

Color Oops is awful.  Get the Color Fix.  If you don't have a Sally's nearby you can order it online.

what do you think would happen if i did the colorfix twice and went over it with a hicolor blonde for dark hair

See where you are after a couple of colour removers. If you are concerned about frying your hair a gentle bleach bath or low vol bleach will be much less damaging than a hi-lift blonde kit. You may be pleasantly surprised at how light your hair is underneath all the dye, the permanent dyes will definitely have lifted your base.

One of my concerns is that my natural hair color is medium brown. So I'm afraid it wont be that light. What do you mean all the hair dye has lifted my hair and it's light underneath? Wouldn't it just all be dark?

Permanent hair dyes work by bleaching out the natural pigment and replacing it with artificial pigment in the new color. So when you remove the artificial pigment with a colour remover your base will be lighter than before you dyed it.

Aaahhhh.... Soooooo will the colorfix still work if I have a million layers of built up dye?

Yes, but you may need to do it 2 or 3 times. There is the possibility that your hair will be a bit stained, so you may not be able to get all the colour out, but you won't know until you try.

Cool, thank you! Will I have to tone? Or should I just post pictures or something when I'm done? I'll be doing it friday/saturday. Also, can you recommend a really good deep conditioner that actually works and that I can find easily? I have a sally's and a walmart.