Studio XPS 8100 not saving files

I've had this problem occasionally since purchase 5 months ago. I'm using Win 7. When I did a Save As on a file downloaded from a webpage the save completed apparently successfully but a later explorer view showed the file as absent. When I repeated the Save As the Save As windows said the file already existed and did I want to replace. I said Yes but still the file was absent after this. A windows search confirmed this absence. When I tried to save on partition D rather than C it said I didn't have access permission (a well-known Win 7 'bug' as I was logged-on as Adminstrator etc). When I did the Save As to a USB stick the file DID save. This failed save effect was repeatable even over a re-boot. I don't have any apparent filing system problems, so was this a Win 7 bug or a confused RAID card on my RAID 0 dual drive set-up? A few others on the web have had Win 7 Library issues. Anyone any ideas?