IE drops connection and can't get on internet without reboot

[Shoop]

My Dell E1505 running windows xp will not stay connected to the internet regardless of whether it is on wireless or wired. I can start downloading something and it will just drop in the middle of it. The only way to get back on the internet is to reboot the machine. The system will work fine but I cannot get back online without a reboot.

I know its not the network because i can get on through other computers.
The motherboard has also been replaced and it still continues to do it.
I have scanned for viruses and spyware and cleaned everything.

Any Ideas?

thanks

[DeaconFrost]

How long do you have online before it drops, from when you reboot? Do you have any firewall software installed?

[Shoop]

Time can vary but it usually dosen't last long. Maybe 10 to 15 mins at best. It seems like when I'm trying to get micorsoft updates it will just drop in the middle of it. I have uninstalled antivirus and firewall software just to be sure. I even installed firefox on the computer. Once IE drops connection Firefox will no longer work. I have to reboot the system to get back on the internet.