it sounds to me to be one of two things:
1) the file is locked a by running process. have you tried memaid? see what processes are running at startup, see which ones are running now, kill anything that looks wonky, and try and delete the file. i find this to be the less likely case, as you've already stated you've hard reset, which would have eliminated such a problem.
2) there's an error on your flash. i believe several utilities will fix this, maybe pocket mechanic? not sure, so if someone does know, chime in. you can also try dells diagnostics program
go to here:
http://support.dell.com/
enter your service tag, leave it on drivers and downloads. next page, click find all downloads. go to diagnostic utilities, and grab the self diagnostic tool.