My computer has an always-on broadband connection using NTL's 2Mb service, but when I leave it alone for a period of time (a couple of hours usually does the trick) it starts behaving really strangely. Like: If I start my mail client, it will check my work accounts, but my personal domain times out, which is odd because my personal domain is hosted at work and the DNS is on the same server as my work address. Also, most HTTP requests time out, but sometimes if I type an address I rarely visit it will pop straight up, and sometimes making these uncommon HTTP requests gets the whole thing going again and sometimes not. Rebooting the PC resolves the problem. Weird.

Does anybody know what might be causing this, or where I might look for the problem the next time it happens? It's an XP/SP2 box, fully patched using auto-update. Internet is via onboard LAN on an nForce2 motherboard, into a D-Link router, but I don't think the router is to blame because there's another computer attached to it which is unaffected, and rebooting the router doesn't improve matters.

Any advice much appreciated.

Try swapping out the driver, especially if you're using a default Microsoft one (unlikely).

Check the event logs (Right Click "My Computer" and goto "Manage". They're under system tools). The contain a LOT of information - but its all very useful to debug this sort of stuff - you never know it might be obvious

Try another LAN card. I used to get network wierdness due to chipset overheating on my MB.