wifi connectivity issue at work

I use my MacBook Pro at work occasionally. My problem is that some days the wireless connects just fine, and other days I can't get it to connect at all and have to connect to the Internet via an ethernet wire. I've run every network diagnostic I can think of to no avail, and we're investigating the idea that something in the building is interfering in some way. We don't have an IT staff per se, so we're kind of on our own as far as computers and networking issues are concerned. As an example, yesterday my MBP hooked right up to the local wifi network at the office and ran fine all day, but today I can't get a wireless connection at all. I'm not a network "expert" by any means, and I'd appreciate any thoughts that may help us resolve this problem.