Internet access problem

I havea very unique problem, my problem is that I am accessing the Internet through proxy very well. Suddenly I am not able to acess the internet on my private ip (192.168.24.13/24) but if I change my IP to new any in the same range like 192.168.24.14/24 I suddenly access the internet. If I give the same ip to other machine it work fien and give me the access to internet. For this I check
1. Firewall of windows - it is off.
2. pinging the switch managment IP and Default getway but not the Proxy server.
3. cable and NIC is ok.
4. Scan for Viruses and now no viruses in the Computer.
please give me the solution I know the problem is in Windows Xp ple tell the problem and solution urgently.