Why won't my hair bleach any lighter??

[pandapopspop]

My natural hair colour is a light brown colour, but for years now i have continually dyed it with semi-permanent and permanent hair dyed in very dark brown and purple colours. Resulting in almost black hair.
A few weeks ago i home bleached it blonde as my aim was to go platinum blonde eventually. It went through the normal stages of being red, orange, yellow etc. But now it seems to be stuck in a very pale orange/yellow colour. Practically white at the top which i want all over, but gradually getting more pale orange as it gets to the ends.
Bleaching it doesn't seem to have any effect on it anymore, can anyone please help me figure out why it won't take the bleach, and what to do now.
Thankyou, in advance.

[terambulan]

the extra strength peroxide required is not retailed on the open market and only available through salons.

[katerich48]

If you live in London there is Sally's (was Ogee's) hairdressing suppliers in Shaftesbury Avenue..they have all the different dyes and peroxides you need..They sell to the general public..