Advice on how to follow up on job offer?

I was offered a job on March initially, but because of the large volume of new hirings, they had to delay my hiring. Now 2 weeks ago, the hiring manager calls and tells me I'm FINALLY next in line for the job and would "probably" start after a week. Now you can guess, it's pretty much 2 weeks and STILL no calls. I've been told that there was a 2 week extension for the previous orientees, which might explain the delay, but they still havent called me! How the heck am I supposed to approach this? I've been trying to get ahold of the hiring manager, but I just cant seem to get through. Is this normal etiquette for job hirings? AND HOW DO I FOLLOW UP WITHOUT SOUNDING LIKE I'm PISSED OFF? Sorry for the long introduction everyone!