Are you still using alkaline batteries? If so, alkaline batteries just don't have the power for more than a few pics in today's digital camera. Some brands may have reached their shelf-life in the store, and may have problems just powering startup
of the camera brand new and right out of the package.
Digital cameras for the most part should only be used with rechargeable NiMH batteries. These days many retailers sell these for around $7 for a package of four (about $15-19 for the batteries with charger). Keep in mind they'll save you big bucks in the long run over alkalines, AND they'll last for at least 100 pictures per charge (and probably many, many more). You'll be very pleased with their performance, and may slap yourself for not buying them sooner. When at the store, look on the package for a power rating of at least 2500 mah.