Canon EOS 30D Instruction Manual page 181

The camera turns off by itself.
Auto power off is in effect.
Press the shutter button halfway. If you do not want auto power off
to take effect, set [c Auto power off] on the menu to [Off].
Only the < > icon blinks on the top LCD panel.
c
The battery is almost exhausted.
Recharge the battery. (p.22)
Shooting
No images can be shot or recorded.
The CF card is not properly inserted.
Insert the CF card properly. (p.28)
The CF card is full.
Use a new CF card or erase unnecessary images. (p.28, 124)
The battery is exhausted.
Recharge the battery. (p.22)
You did not focus well. (The focus confirmation light <o> in
the viewfinder blinks.)
Press the shutter button halfway again and focus the subject. If
you still cannot focus properly, focus manually. (p.30, 80)
The LCD monitor does not display a clear image.
The LCD monitor screen is dirty.
Use a soft, lens cloth to clean the screen.
The LCD's service life has expired.
Consult your nearest customer service center or dealer.
Troubleshooting Guide
181