Unfortunately, this is like telling a mechanic "my car won't start". There are many things that could cause something like this. Hard drive corruption, memory fault on PC, file corruption, virus,something else running on the PC, etc. Or, it could be something very simple. Shut down all other programs running on the PC. Run the error checking tool in Windows and a virus scan if you have one installed. Try doing a defrag of your hard drive, trouble there will indicate upcoming hard drive problems, if that is, in fact what it is. (It's a good idea to do that once in a while anyway) Worse case scenario is that you have to reload 3CX. Try to get a copy of your last backup off the hard drive and move it to a USB stick or burn onto a CD. I, myself, do all backups onto a USB stick (and a copy to a second stick) in the event of catastrophic failure of the the hard drive.