Solution 1: Pushing down the button above the camera flash
First take off the back door of your BlackBerry Bold phone. Then push down the small plastic button (white or light gray color) that’s located above the camera flash. You need to have a very careful look to see it, as it is very small. There's a small opening above the camera's flash and it is roughly 1 inch long and 1 mm tall. The button that you need to push down is located right in the middle of that opening. You may push it down using your finger nail or a little pair of scissors. Once you do it correctly your sounds will be loud and clear.
Solution 2: Placing a thin piece of paper behind the battery
The back battery cover of the BlackBerry Bold is very flimsy. Therefore, when playing media files, the battery cover can collapse in and it may cause the phone to press on the mute. Otherwise there might be a notable decrease in volume.
As the solution for this sound issue, insert a small and thin (less than 1mm) piece of plastic or paper at the top of the battery about half an inch from the bottom of the camera’s location. If your phone won't ring try this and it will resolve the issue in most cases.
Solution 3: Pulling the battery out
Another solution is to pull the battery of the BlackBerry Bold out while the phone is turned on. Then wait 30 seconds and insert the battery again. Your phone will reboot and the problem will be solved.
Solution 4: Updating your BlackBerry software
Often this BlackBerry Bold won't ring issue can be solved by updating the software of the phone. In fact this is a very good recommendation for most of the problems you may encounter. Because many issues for BlackBerry phones, such as the BlackBerry Bold 9000 and BlackBerry Bold 9700, are software issues. First you need to download the latest version for your BlackBerry phone and from the carrier the phone was sold with. It might take about 40 minutes to download. Next connect the BlackBerry using "Application Loader" (this is built into the desktop manager that came on the CD) and push the new software on to the device. Make sure to click on the "Advanced" box and check both check boxes to remove all currently installed software. For detailed guidelines read this illustrated guide about performing a clean reload of a BlackBerry device. If you have any important data in your BlackBerry phone you will want to back up first.