Rice cooker goes to "keep warm" mode before rice is cooked

The Manual for the Rival RCS200 Rice Cooker can be found here:
http://www.rivalproducts.com/manuals/MANUALS/RCS200_43_68557881.PDF
Make sure you are following the directions for the correct amount of water to rice.
It could be that your unit is not switching from cooking to warming at completion of the cooking cycle. It should automaticaly turn to the Keep Warm Setting when it detects a temperature of 212 degrees F.
The manual advises that there are no servicable parts. If this is a new appliance I would recommend returning it to the point of purchase. If this is not possible try contacting Rival Customer Service to see if they are willing to assist with replacement or repair: See here:

https://secure.rivalproducts.com/ContactUs.aspx

You're probably using too much water. Rice cooks primarily while sitting in hot water, not while its boiling. That's why the cooker switches to Keep Warm so quickly. The correct way to cook rice is to pre-soak the rice for about 30 minutes, drain to get rid of the excess starch, combine the rice and cold water and bring the water to a boil and turn off the heat and let it stand for 15-30 minutes. That's why*- rice cookers take 45 minutes or more.

Warm mode probably isn't going to cook anything. It's just to keep things warm.

Instructions quoted from the Durabrand Rice Cooker model HRC 18G manual...... 1 cup of uncooked rice rice will make about 2 cups of cooked rice. Add rice to the inner pot. Maximum four cups uncooked rice for the model. Many varieties of rice can be used including basmati, wild rice, arborio risotto, saffron rice and long grain rice. Whole grains, such as barley can also be prepared with the rice cooker, follow instructions on the package.

For every cup (160ml) of raw rice, add 1-1/2cups of water. For stickier rice add slightly more water, for fluffier rice use slightly less water.

When your rice is cooked, the cooker will automatically switch to the warm function and the yellow warm light will turn on. The cooker will stay in the warm function untill is disconnected from the wall outlet. The cooker will keep the rice warm 158F - 212F

Hope this helps, its quoted right out of the manual I have for my cooker

try adding a little less water, And letting it sit about 4 min to make sure the steaming has stopped

I just fixed our rice cooker with the same issue - turns on and warms, but won't stay in 'cook' when the lever is pushed down. My solution was: the pot that goes inside the rice cooker was dented on the bottom and was not pressing down on the mechanism at the bottom of the cooker. Once I flattened the bottom of the pot, it works!

most cookers have a basic lever down to cook/ up when rice is done or warming

2 cups med rice 3 cups water yeilds about 6 cups cooked, allow rice to sit 4 -5 min after cooking to allow to finish steaming

well your rice cooker needs to be replaced.. if you still want to use it, then have it fixed by a technician coz it needs electrical expertise to handle the wirings inside it..