Losing Internet Intermittently

Hello,

I am running XP SP3 on a Dell Precision M6300 and when it's been up for a while, it loses its connection to the internet. I normally run it wired to a Netgear switch in the same room which in turn is wired to another switch downstairs and thence wired to the BT Home Hub 5 internet router. Whilst it's misbehaving, I can still ping my router from it and all other connected devices whether wireless or wired seem to work OK at the time (Dell Dimension 4600 PC in the same room, Kindle Fire, Nexus 7, iPhone, Samsung phone). If I swap it over to a wireless connection it works for a few minutes and then goes again and then going back to the wired connection it still won't connect. A reboot fixes the problem for a while although this while seems to be fairly unpredictable, sometimes hours, sometimes days. All internet connections are affected (Firefox, Chrome and IE browsers, Outlook email etc.). If anyone has run into a similar issue, I'd be grateful to hear how it was sorted. If you need any other info, I'll happily supply it but I must confess it's driving me nuts.

Regards, Gerry