How would you handle this?

I was offered a job at a clinic, a place where I also did a preceptorship at during school. They brought me back after graduation and interviewed me. After the interview I was told about a f/t position that was open, and if for some reason that didn't pan out I would at least be on a PRN status between the 3 clinics in this area. Which I was more than ok with. It's been 3 weeks. In that time I've taken my drug test, got my background check going, and hearing only twice from the HR lady who I've been talking to. When I leave her messages she doesn't get back to me. I've been calling practically every day but she's either "not at her desk" or "in a meeting". Last time I talked to her last week, she said she would call me THIS week and I would interview with one of the doctors. I didn't hear from her at all this week. Left messages, no call back, even though I know she was there.

So I finally said forget her and I left a message today with the DON (who I also interviewed with and she is familiar with me and my work), asking her to call back. any call back? No. My mom works in a hospital and she brought up my situation with her HR person to get her advice. The HR person told me it's unprofessional and unacceptable, and that I should go to the clinic in person on Tuesday and ask to speak with the DON.

How would you handle this? Would you persue it or give up? Would you go to the clinic in person without an appt? (I don't want to come across psycho..). I want this job more than anything; I get along with everyone there, the nursing staff pushed for the HR lady and DON to interview me and hire me, during the interview they seemed eager to hire me as soon as possible, and now I just feel like it's all falling apart. I don't appreciate being ignored. If they don't want to hire me for some reason, at least have the decency to tell me, especially if you've already offered me the position! I've been assuming I would start and financially it's starting to have an effect.

Any and all advice appreciated.