I have a 97 Ford taurus. there are days when it will not start and then it will start for 2 or 3 days and then it wont start again. what could be wrong with it.

If you do not run it low on fuel, and it is over 20 years old, There can be many ways you experience loss of spark or fuel. The technician would need the vehicle to experience the same conditions and be connected with his test equipment during the event. The memory codes in the vehicle's computer can sometimes help. But in your case, you have one that has to be acting up. Another approach would be the Ford garage, They can test ways that others cant because of the types of test equipment and methods. Their experience with weeding out problematic aftermarket parts and updating motorcraft parts to the current trusted date code can be the very thing your car yearns for.