Does this happened to you before ?!
The domain yourwebsite.com has reached its bandwidth limit.
Please contact the system admin as soon as possible.
If you still attached to hosting that offer limited bandwidth like 1GB a month, 10 GB a month. Mostly like you are attached to a hosting reseller. Reseller are small hosting company who buy 1 hosting account from a supplier and cut into pieces before resell it to their customer.
1) Move to other host
If you uses lots of bandwidth, you should consider move your website to a first tier web hosting company who has full control of their datacenter and hardware.
Most first tier shared web hosting offers unlimited bandwidth with “fair usage” condition in their T&C. While dedicated server hosting has better “guarenteed bandwidth”, which means if you have been given 300GB, you will have it but not more than that or you have to pay.
2) Contact existing host for a free bandwidth upgrade.
Call, email your host for immediate bandwidth upgrade, for free !. This is the easiest way, your website can up can running immediately. Usually some 10GB ~ 50GB bandwidth cost almost nothing to your hosting reseller, if they charge you handsomely, consider switch to other host.
3) Remove videos, large files.
Check your log file, if you have a very large video files or any files that take up a lot of your bandwidth, consider move to some file sharing website. Moving those large files to file sharing sites has many advantages, including a) Faster download b) unlimited bandwidth c) some are free d) some pays you for offering many downloads.
Don’t forget you have a friend who is video friendly, http://www.youtube.com
Anyway, having bandwidth exceeded is a good news, that means you have more visitors to your website now! Consider switch to other host if you have to !