Dedicated Linux Server help

We operate a few websites using a dedicated server through FDCServers.net. Our server has been crashing on us at random for the last few months, on multiple servers with different companies, leading us to believe that this is OUR problem and not a problem with the hardware/hosting company. Our server is down again today and we need someone who is experienced with Lynux/Cpanel who can help us figure out our problem and make sure our server is configured properly so it will stay online ALL the time. We think our current problem has to do with GD library, however, we are not certain because our error_log file doesn't have any issues when accessing via SSH. If you can take a look and let us know how much $ it would be to correct this issue. We make our money off of ad revenue, so the longer our sites are down, the more money we lose.