I don't believe it is the resolution that is causing your render to freeze. You should try rendering it at a very low resoltuon to check that. Usually when a render stops it is because of a problem with a particular object or shader. You have to track down the offending object. You can check off the invisible box and see if it renders fine without certain things.

  A lot of new people here seem to be having inordinately high render times. I'm not sure what they are doing. I produce images for large format on a regular basis and I've never had to render an image for more than a day. I think people are perhaps increasing the object and shadow accuracy or setting certain features to the highest setting which is unnecessary. Carrara can render to around 16,000 pixels in each direction. The larger you go, the less high the resolution needs to be. Anything that is over 3 feet does not need to be 300 ppi. When they first started printing billboards, the standard resolution was 7 ppi. That's right "7". Even now a billboard looks great at 35 or 40 ppi even though the printers are capable of higher res. Most people now set up a billboard at 1" scale and 300 ppi. Posters at 3' x 4' look good at 150ppi or 200ppi. A render that is 2500 pixels x 2500 pixels looks pretty good when printed at 4' x 4'.

Here's a photo of a Carrara render printed at almost 4' x 4' on plain paper. It is only a little over 2,000 pixels wide. You can't really tell but it is not pixelated and the trees in the far distance still have good detail. It is actually quicker to render at a higher res than to set everything on maximum and usually it will look better.