iMac fans stopped, what must I do?
You should certainly request help online or through the phone - (31) 0900 7777 703 - in either Netherlands or the country where your mac was originally sold. Fans are pretty easy to diagnose remotely since it's almost always the fan unit failing (or when it's not that, the next most likely cause is simply reconnecting the fan cable) so you can often ask for a parts and labor quote to help you decide what to do.

You seem to indicate it's the CPU fan. It and the hard drive fan are very hard to replace as you have to disconnect and remove the LCD panel, the logic board and many of the other parts. The optical fan is more amenable to a DIY repair. All the connectors are very delicate and if you break them, the cost to repair can be pretty large. (Think $800 to $1100 for a whole logic board). iFixit.com has good take apart manuals and once you have a quote or two from authorized service providers, you might decide to get inside to reconnect the cables and at least look around.

My advice is don't do anything yourself until you're sure Apple won't cover it by calling them first to get a quote. The main hardware warranty has great links for getting service worldwide - since it's quite long I'll pull the links here for quick reference:


International Support Information 
Apple Authorized Service Providers 
Apple Retail Store 
Apple Support and Service Phone Contacts Worldwide 
Apple Complimentary Support


Lastly, don't be afraid to run it for short time and low CPU use to get more information and be sure which fan went out. The CPU will reduce clock rate when it gets warm, then it will go to sleep for 30 seconds if that doesn't keep it cool, next the OS will shut down (all of the above events get logged at default settings except maybe the clock rate). The CPU will also shut everything off abruptly if all of the above fail. Don't run for weeks or hit the CPU with 100% tasks and expect it to last for years with the CPU fan off, but other things will have to fail for it to be a melt / fire hazard issue. I also wouldn't run it needlessly and risk MLB failure needlessly.