Any noises during the freeze?. One possibility is a bad disc spot, which can retry reading (or writing) for easily a minute. There will be a continual clicking if this is the case.
Actually, to help you we need a great deal more information about your computer (for instance you don't even say what operating system you are using!). Most important, we need to know what is happening when the freeze occurs, are you gaming, on-line, downloading, imaging, and if on-line to what?
There is always the possibility of a virus infection, and we need to know if you have any protection in place; if so, what, and is it up-to-date?