I dont know what has happened to my front brake, the last 100 times ive ridden I havent even had to look at it and its been fine, but today just as I was about to set off I noticed that something wasn't right. Basically, the right hand (looking from the direction of the saddle) brake block is resting against the rim, meaning the left block is a fair way off the rim. Normally of course I would just assume it had been knocked and push it back into place, but everytime I try to push it back it just falls straight back into the same position. Its like the whole brake system has fallen loose overnight. Any suggestions?