Disable LAN but keep the Internet accessible ?

I would think it's probably just a firewall that doesn't allow intra-network communication.

If you want to talk to other computers on your network then you have to go through the router. If the router is disallowing this type of communication then you get the result you described.

I'm not really sure how they set it up to do that, but it's just a matter of configuring the router such that it will route the internet to each computer, allow the computers to send data back (to the internet) but when you try to say ping somebody at 192.168.1.2, this type of communication would be disallowed.

Edit:

No, I'm pretty sure intra-network communications should have no effect on internet speeds.

The only issue, is if it's a large LAN. Basically, the communication has to go through the router, so if the router is busy all of the time, then YES you will see a performance drop.

Basically, your LAN (ethernet) should run at 100Gb speeds (or greater). That's at least 100 times faster than what your internet can provide. So the data being sent shouldn't slow down the network...again, unless you're running like 10 computers through a single router and doing some serious LAN gaming. Then it would likely overwork the router and you get network congestion in the LAN...I think.

So it's not actually the internet that's slowing down, it's just the ability of the router to serve the internet to all of the computers...because it's trying too hard to serve up data for the LAN game.

I would base my final analysis on empirical data. If when y'all are gaming, the network slows down, then I would agree that it's likely the LAN-party that's causing the network congestion.

Create an access list in which each computer is only allowed to access the internet. You guys are behind a firewall, and the only traffic that the firewall allows through it is that going to the internet.

he's in search of a psp, no longer computer.... besides.. i imagine you go with a converter, convert it to a commonly used mp3 or maybe with.... and then if want be to a psp format, notwithstanding for music i imagine mp3 works. i imagine you want to remodel video to a psp format. do not bear in mind bought mines...

LAN chat/messenger/conference is disabled.
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Used in some auditoriums/wi-fi hot spots/etc for the same effect at on your campus.
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There are quite a few different ways. The simplest way is simply to place a firewall rule on each computer that blocks all traffic to or from other computers on the LAN. Another way is to put each computer in its own VLAN and configure the router not to route between VLANs.

Yet another way is to place a firewall rule on each computer that blocks all ARP replies. Then you just statically configure in the router's MAC address. This way, the computer cannot determine the Ethernet hardware address of the other computers on the LAN and so cannot address packets to them on the wire.

Update: Oh, you didn't mention that it was wireless. Wireless access points have an option to disable host-to-host traffic. They've simply enabled this option. And you are right, LAN gaming won't affect Internet access. So whoever disabled it is either misinformed or gave you a lame excuse. But I think you are mistaken. You can't tell if two computers are in the same LAN by looking at their IPs. If they're wired to different routers, odds are they're not in the same LAN at all. (But in two different LANs that use the same IPs.)

Hook up just your modem.