1) Welcome to the Party!
2) As you are obviously new here, I have some suggestions to help us all help you:
When you post, please post your entire configuration including (but not limited to) your installation method (7.X.X?) and vicidial version with build (VERSION: 2.X-XXXx ... BUILD: #####-####).
This IS a requirement for posting along with reading the stickies (at the top of each forum) and the manager's manual (available on EFLO.net, both free and paid versions)
You should also post: Asterisk version, telephony hardware (model number is helpful here), cluster information if you have one, and whether any other software is installed in the box. If your installation method is "manual/from scratch" you must post your operating system with version (and the .iso version from which you installed your original operating system) plus a link to the installation instructions you used. If your installation is "Hosted" list the site name of the host.
If this is a "Cloud" or "Virtual" server, please note the technology involved along with the version of that techology (ie: VMware Server Version 2.0.2). If it is not, merely stating the Motherboard model # and CPU would be helpful.
Similar to This:
Vicibox X.X from .iso | Vicidial X.X.X-XXX Build XXXXXX-XXXX | Asterisk X.X.X | Single Server | No Digium/Sangoma Hardware | No Extra Software After Installation | Intel DG35EC | Core2Quad Q6600
3) "stopped suddenly" is a vague description. Did the agents all lose their audio call and find that their browsers stopped working for Vicidial? Or did all the client calls drop? What exactly happened. You can say it in layman's terms, but try to be descriptive. (Technical jargon and terminology isn't necessary, but "it don't work" is hard to diagnose, lol). I'll assume for the rest that the agents lost audio (calls ended) and lost their web page connections as well.
4) Is this server at your location, or is the server in a different physical location?
If it's elsewhere, it's possible that your internet connection to the server is not stable. Loss of internet connectivity between the agent site and the vicidial server site is impossible to fix in the Vicidial server itself. You must have a stable connection to use Vicidial. This can also happen if someone overutilizes the internet (you got someone on Netflix in the office?)
If it's at the same location, then the local network could be unstable.
More details ... we'll be able to help you more directly.