It probably isn't (wasn't) hardware. Occasionally the problem can be associated with a certain program, but there's still an underlying problem with the OS. Don't believe me? Google this: "windows 7" "not responding". Include the quotes. There are over one million hits! When is MS going to address this ?!?!!? I'm REALLY sick of having to fight with this issue on my users' computers.
Its less a Microsoft problem, more a third party software issue. Windows 7 and the NT kernel as far back as NT 4.0 (in my experience) is rock solid. The main stability issues relate to hardware, or drivers. Programs not responding are often related to poor code in those programs. Anyone can write an app, including those who know just enough to make an app work, much less the intricacies of memory management, good networking, or proper security.
Hard locks where the system just freezes solid tend to be memory (RAM) issues. Other crashes can be harder to troubleshoot. Bad sectors on a harddrive, video card instability, a virus, etc..
As for the OP, the quickest fix, to at least help isolate the problem is a fresh install. It could be a million problems on a dirty install, so installing fresh narrows it down significantly (almost to hardware exclusively). It also eliminates the possible problem of 3rd party drivers (the Microsoft drivers are typically very stable).