AF-assist beam
Many PowerShot camera models employ an Auto-Focus assist beam to aid focusing in lower light. If this beam is blocked the camera may have difficulty focusing.
Be careful not to block the AF-assist Beam with fingers or other items. Try using a tripod or other stable support, and use the camera's self-timer to ensure that nothing is blocking the AF-assist beam.
The beam is usually located near the flash unit or viewfinder as shown below.
*PowerShot S80 pictured