Garden Solar Lights no longer light up :-(

[diandpat]

Don't know if this is the right place to ask this and if it is not please feel free to move it.

This is probably a really stupid question but I have those solar garden lights in front and back yards and there are only about two of them left that actually light up. I have only had them for two years. Are they finished or is there a battery (?) or something I can buy to make them work again??? I really really like the ones in the back garden as they change colors and I looked for more this year and could not find them.

Is it hopeless or is there hope?