Why won't my A540 start after I replaced the batteries?

My camera will be three years old Christmas 2009. I have replaced the batteries before and haven't had any problems. The camera was working fine before I removed the batteries because of low battery.

What kind of batteries did you replace them with? It may be that you replaced them with batteries that are just underpowered. Digital cameras need batteries with an "mAh" of at least 2500 to get proper performance. There's also the possibility that the batteries you replaced them with are dead or have been on the shelf for longer than you realize. This can drain out the batteries to the point where they just can't power the camera. This largely happens if you buy batteries from large discount stores in bulk, like at Costco.

Lastly, you could try cleaning your battery contacts with a pencil eraser. They do get greasy and dirty and to clean the contacts when you replace the batteries is a good habit to be in. Outside of that, if you live in a humid area, it's possible that the camera is suffering from moisture. Putting it in a ziplock with a cup of uncooked rice for a day or two will draw out any excess moisture gumming up the works.

If all that fails, it may just be serendipitous and the camera just needs servicing.