Why do I eventually lag and have to restart during a match?

[Destroyer20000]

I have been playing on a server with about 10-20 people on constantly for about an hour now and after playing for a while, I start to get computer lag (almost 100% sure it's not my network) which makes the game unplayable which forces me to close the whole game and open it again if I want to play properly.

I find this very annoying because I commonly get switched to the opposite team I have been playing on for most of the match (about 3/4 of the match is finished when I start to get lag each time) and I hate playing on the opposite side of a game after I've been playing on one side for most of it.

My laptop (which used crappy integrated graphics) needs to have its HDD scrubbed and Vista (trying to switch to XP, but doesn't find my HDD partition) reinstalled because my laptop is beginning to go very slow now, but I wonder why I only get lag about 3/4 way through the match and now as soon as I join? I get pretty much ZERO computer lag (I say computer lag so you don't get confused with my network lagging) through 3/4 of the match, but after that, it's unplayable.

I have my FPS turned down to the "MY 486 OWNS U" setting or whatever it's called (although I don't really understand how this works because I still get 60-70 FPS normally) and I have it set to very low detail (one selection above "Horrible" if it has a different name to "very low".

If you have any ideas why this might be happening, please tell me.

Thanks.

[Fate]

When you say "computer lag", do mean having a low frame rate (fps)?

[Destroyer20000]

When you say "computer lag", do mean having a low frame rate (fps)?

I mean where there is a low FPS, yes.

[Gibstick]

Doubt it's overheating since it's fine as soon as you restart the game. If you can, turn down some settings in the gfx control panel of your integrated card. Also try playing with vsync on (type /vsync 1).

[V-Man]

Run AC and hop on a server, then take a look at your RAM and tell us what it's doing then.
1) RAM total capacity
2) Initial AssaultCube RAM usage
3) RAM usage when AssaultCube starts to lag up