[Cannot edit my profile, please help!]

I mean log in SL client, rightclick avatar, profile, change About description, click OK.

Not on the website.

[Cannot edit my profile, please help!]

Ok, this probably sounds a little basic but...

When you try to change inworld,

did you click the OK button instead of clicking X?

[Cannot edit my profile, please help!]

Maybe try entering a shorter description first to just to test if the problem is actually because of the length?