The money may have been committed in a budget passed over a year ago. If the school does not allocate it, it loses it. there is only a certain amount of leeway in how much of certain finds can be moved over to other funds. So, if you have been given a specific budget for school rebuilding (as many secondary schools have) then you can't decide it's better to spend it on books or computers, even if it would be more sensible to do that.
However, all this is information that is in the public domain- you are entitled to answers under the freedom of information act - so I would get your Student Voice group to express their views urgently to the chairman of governors in the first instance. Nothing concrete is to be gained from sounding off here, unless it makes you feel better. Make real waves by complaining properly to people whose job is to make a difference to your school.