I have a Pentax K-r. It works fine in general. But, when I try to use flash, it doesn't take pictures anymore. The shutter will not fire.
What can be the possible causes? Is there a hope to repair it?
Check the custom option "Release While Charging". Check the batteries (camera and/or flash)
If the option is not checked, you will not be able to take a picture until the flash is ready.
The flash can take some times to charge if the batteries are not fully recharged (both for the internal flash and the external flash).
Check the manual at pages 81, 150 and 309 : http://www.ricoh-imaging.co.jp/english/support/man-pdf/k-r.pdf