hi every one
i have a strange problem, i have XP SP3 and i can logon to my ISP account but i can't browse the internet, and the tow computers icon in the system tray still balck for a short time then i lost the connection, i scanned my system for viruse and spyware and every thing ok

NOTICE:
1- i have too vista ulimate sp2 on the same computer and use the same ISP account, i can browse the internet very well. so what the matter with XP
2- i can't use the safe mode for xp

When you try to browse internet from xp, what is the exact error if there is one?.

May be you can try after disabling any firewall installed in your computer.

Have you tried to reset the IP stack. Might help your problem

I had the same problem recently. I found the firewall I was using had started blocking my DSL modem. I deleted the firewall and have had no problems since. I was using Sygates free firewall.

Two things you could try are running Combofix, and LSPfix. Both are d/loadable from the net for free. There are a number of malware programs that aren't picked up by Virus Scanners.
When you use Combofix you have to disable resident virus protection, then the program automatically runs and removes malware.
LSpfix will show winsock2 stack errors. Check out the web site here
http://www.cexx.org/lspfix.htm

Dave