Fixing An Older Installation

Upon leaving my last company I was given one of the older laptops (too old for anyone to care to use anymore), an IBM/Lenovo ThinkPad. The laptop was purchased with OEM licenses for Windows XP and Office. I have not reinstalled XP on this PC, and although I no longer can connect to my old company's domain, I have been continuing to use the PC by logging on to the domain, as I am not able to log onto the PC in any other way. This is, by the way, annoying for me, because I can access the internet but cannot access my other computers at home since they are not on the "company" domain and so I do not have permission to do so.Now the problem: This laptop is beginning to have some sort of problem, where applications like Firefox just suddenly freeze up and cannot be terminated, not even using Task Manager. I need to hardboot the machine each time as I cannot even shutdown in a normal fashion.

So how is the best way to a) fix this problem and b) get permission to log on to the machine "locally" and not on the company domain? One thing I am thinking about is just re-installing the computer, and I have the Windows XP license info on the label on the bottom of the laptop, and I suppose I can get the office license key using something like ProduKey. It would be nice to avoid having to do this, however, as I do not have the Lenovo CD's and would have to reinstall everything from the net. Any advice on what is best to do? How to find/fix the freezes of software like Yahoo and Firefox? How to get away from the company domain? I as user have admin priviledges to the PC but cannot, for example, touch the antivirus software and that is irritating.