iMac 27" Duo start up problem

Hi, could any iMac experts out there help me with this one please? I have always been a window user and this is my second day with my brand new iMac. The shop delivered and set it up for me yesterday. Today, when I tried to switch it on, the first time, no response (just a white screen). Switch it back off and on again, then it took 10 mins to boot up! I called the shop and they said it might be the RAM (i upgraded from 4GB to 8GB) having a compatible issue and said if the issue continues the next few days, they'd send a technican to change the part for the RAM. I shut it down and tried again, again just the boosting sound then a white screen, nothing. Switched it off and then back on again, and again this time it took 10 mins. What should I do? Let the shop changes a part (as they suggest?) or should I insist on the shop giving me a new machine?

Normally, if memory is incompatible the machine will not boot at all. Or you may even get a constant beeping noise. A white screen and 10 minute boot time indicates other problems in my opinion.

Since the machine is brand new I believe I would insist on them bringing out a new one to replace the one they sold you.

Regards.

Thanks, chscaq. Is there a thing as "Apple ram". I wonder if they've given me some cheap brand upgrade?

Ah, is that the problem? I read the manual. It says you should shut it down only when you're not using your mac for more than a few days. You should normally just put it to sleep. And I SHUT IT DOWN. Does the iMac take ages to switch on from a SHUT DOWN mode (not from a sleep mode)?