When I try to connect to a lot of site this sentence appear on the page: You have tried to access a site that has been blocked by the 3Com Router. Please contact your System Administrator to have this site authorized. How I can unblock this site?

Open the links in browser. Need more information on which device is being used, etc.

Talk to your system administrator.

When you enter the URL: http://www.facebook.com; and there is no web page appearing, the following could be the problem;
1. Maybe the you are missing out something in the URL you are entering (missing some character) or there is some case problem (all the letters should be in lower case).
2. Maybe the internet access connection is limited or very low. Please check that your reception is good enough.
3. Your PC could be blocked from accessing that site. Find out! You can also check with your internet administrator - if you are just unauthorised to access the site then try another system network.

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there you are
http://download.driverguide.com/driver/3cxfe575bt/3Com/d112287.html

Unless, you can try another computer to connect or there is a tiny (and I mean sometimes pinhole) reset button to push, it may have seen its last day. It has happenned to me and I picked up a little 35 dollar Belkin that worked great.

my facebook was blocked by 3Com. How to unblocked?
the error is coming out is.

You have tried to access a site that has been blocked by the 3Com Router.

Please contact your System Administrator to have this site authorized

please help me on this problems.

SHIVA

there's a few possibilities that might cause this problem.
First thing that comes to my mind is your wireless control access to the router's network.
In order to get through things here you need to get into the router's interface (http://192.168.2.1) using your password (default is admin), from their you need to get into wireless (b.t.w - I'm sorry if I'm not accurate here, I'm not in front of the router right now).
After getting into wireless you need to see if there's a control access tab in it (if not it might be in advances settings at the left main menu).

if it point to prevent... the problem is not about access control, otherwise you need to enter your MAC address in the table below, before putting any MAC address I will like you to tell me if it's on prevent or permit option.

You have to configure the WDS on the 3comm, configuring it to the MAC ADRESS of the BT router (if it is wireless), if not connect it by ethernet and set the 3comm as WDS allowing the other 3 more u want to add as acepted MAC ADRESS for access points.

Hi,
This could have a number of causes. However, you could try adjusting your MTU settings, since this can cause problems with accessing msn and similar sites. You can do this from within the router user interface.
You may well have tried this already. If not, experiment gradually with reducing the MTU setting towards 1400 - see this link for a quick tutorial (though not your router model, I know).
http://kbserver.netgear.com/kb_web_files/n100603.asp
For safety, of course, please back up the registry, or set a system restore point, before trying this out.
Other 'fixes' depend on your OS and security settings. However, since the problem does seem to be within your new router, you might find more information on the 3com knowledgebase.
http://knowledgebase.3com.com/

Are you cable user? register the modem's  mac address to Internet service provider.

make sure that the Local area connection IP address of you PC  is not static.