Should you need to repair a solar light, it’s important to know that all of them are not created equal. Henceforth, the instructions will generally not be the same; but there are a few trouble-spots that are fairly common to all solar lights.
It’s a good chance that it’s something as trivial as a bad battery. And wait–before you go and buy another expensive battery–check the battery contacts and the terminals on the light fixture. Make sure there is no corrosion, rust or oxidation (white, flaky material) on them. For rust and corrosion, sandpaper is generally good to use. If you have corrosive materials on the battery and/or in the battery bay, use a soft tooth brush to brush away the flakes.
If that does not do the trick and if you have a multimeter handy, hook the batteries up to it and see what kind of charge (if any) the battery kicks out. If they register correctly, place them back into the battery bay, and take the unit to a dark room to determine whether or not it works now.
Also, unscrew or unhinge the glass covering for the photovoltaic-cells (the solar board itself). Soak the glass in soapy warm water, dry it good, and replace. If it still yields no activity, get a new set of batteries (should be either nickel-cadmium or nickel-metal hydrate—make sure you buy the same one that your old one is labeled as). Again, if it’s daytime, test it out in a dark room.
If it still shows no signs of life, then it has to be the solar panel itself. Most likely, it’s a dead photovoltaic cell (or even two). Unless you have experience with soldering irons, it’s better to go ahead and replace the fixture.
***Special note: Never submerge any electrical part of a lamp in water while cleaning.
Great Solar Yard Lights is an online source for information about choosing and installing solar lighting for your home and garden.