1) Does on board computer have a registry or contain a file(s) that keep the history of programming changes, so that if the software was altered and then returned back to its original state that this could be deleted by diagnostic equipment?

2) Can diagnostic equipment detect software changes?

I have been using Microsoft Office 2007 Professional Plus for nearly a year now. I’ve always been able to run every aspect of Office without fail. I haven’t changed any hardware or significant software changes in that time, but within the last few days, it has quit working. Whenever I try to start Word, Excel, PowerPoint, Access, or Outlook, I get an error message saying that there isn’t enough memory or disk space to run those programs. I can run every other program on my computer without problem. I have twice ran the Microsoft Office Diagnostic tool, and it says there is no problem with my system. My anti-virus, anti-spam, and anti-malware tools can’t find anything. If I contact Microsoft about the problem, their free troubleshooting help doesn’t apply to me. They want to charge me just to CHAT with someone who may or may not be able to help me. I don’t know what to do to fix this, but I don’t want to pay them money. Please, can anyone offer any suggestions?
Canadian Bacon’s answer fails. The processes that are currently running on my PC aren’t taking enough memory to cause a problem.