[Marco64Th]

The server load is not for only your site, but for all sites hosted on the same server. So how many people are online on your forum is for the server load irrelevant.

As a rule of thumb for good performance the server load should stay under 1 for each CPU in the server (so if you are on a 2 CPU server, the load should stay under 2). A load of 9 is pretty high for most servers and will probably result in slower load times. A load of 50, as others say, is a level where a server becomes really unresponsive and it might be even difficult to get a response on the commandline.

You could do the following test:
- Turn off your forum for 15 minutes.
- During this time monitor the server load. Best to do from cPanel/Plesk or such if installed. Note the numbers.
- Turn on your forum again.

Contact your host support with the numbers you collected and ask them for an explanation if the high serverload. If they try to blame your site for it, explain that you have measured these numbers while your forum was offline, so it can not be caused by your site but must be from another site hosted on the same number.