Help! Server returning blank pages

Hi all, I apologize if this is the wrong forum. About 25% of my sites pages are being returned blank to the browser. I get the same result if I strip the code down to "<a>hello</a>" AND if I delete the page entirely from the server. Strangest error I've seen in 8 years. So I'm confident it's not a coding issue. My problem is, the system admin in the other building always thinks it's me. :-) I know we're running IIS 7.5. Does anyone have any ideas what might be causing it? Thanks in advance, Josh