I'm trying to fix an old laptop running XP, it was all working fine until fairly recently but it will no longer connect to the web (via Chrome, Firefox or IE). I can ping out to the IP address for google, yahoo, etc. and ping the DNS server that ipconfig tells me it is using and works when accessed from other laptops but nslookup fails giving 'DNS request timed out' errors.
I have tried disabling the firewall but it makes no difference. The same problem occurs with both wired and wireless connections but both work with other laptops so it's a problem with the laptop itself not with the internet connection it is trying to use. It has the same problem trying to connect via a completely separate connection too.
Unfortunately, I don't have any XP disks handy so I can't try a repair install and someone had the great wisdom to disable system restore points on this laptop so I can't try backing it out to a restore point.
What can I try next? What could be the problem?
Edited to add:
Ping to google.com doesn't work, ping to their IP is fine
DNS settings are coming from the ISP, and work fine on other laptops, replacing them with public DNS server settings doesn't help.
Telnet to the DNS server works from other laptops, but not from the laptop that is not working. I tried RootkitRevealer but it showed nothing untoward.