Word randomly won't open

Randomly, Microsoft Word will not open. It will open and function just fine for several days or a week or so. Then for no reason that I or techs can determine, and without warning, it will not open. If it's already open, it won't save the document I'm working on, and will only let me exit the program. Then it won't open. It says it can't open because there is insufficient memory or storage space. This is false. I have 6 GB RAM and over 100 GB free disc space on Drive C where the OS is installed. (I know that XP can only use up to roughly 3 GB RAM, but when this happens it has never been using more than 1-2 GB.) When I disable anti-virus, Firefox, Outlook Express, Roboform, and virtually every other running program, it still won't open. I have changed Processor Scheduling back and forth between Programs and Background Services. I have changed Memory Usage back and forth between Programs and System Cache. I have changed Paging File sizes numerous times, including "system managed" or "no paging file". Nothing fixes the problem. My computer is relatively new. It has an i7 processor, Windows XP Pro, and 6 GB RAM. The hard drive is 1,000 GB, partitioned as Drive C (128 GB, 100 GB free), and Drive G (803 GB, 777 GB free). I also have an external, USB connected 600GB drive (513 GB free). All are healthy. All three are formatted NTFS. I don't know if this could have anything to do with the problem, but sometimes on start-up I get the message (3 times, I assume one for each drive) NTFS disc check not found, so disc check is being skipped).

Can anybody help me out on this? It is driving me crazy, and at least three or four techs have not been able to figure out the problem or how to fix it. Thanks. Gilbo