Unable to attach files to email

Hello,

My father is unable to attach files to out going emails, via Gmail and yahoo. He's tried different browsers, and it's the same thing. He's reinstalled Java and Flash, and he's run several scans for viruses. He checked his firewalls, and even disabled them. He went to basic format in Gmail. Nothing is working. The only size he can is under 100K. We've tried everything we can think of. We've researched it. Nothing. Can someone please help? His operating system is the XP. He has AVG for his anti-virus program.

Thank you in advance.

Shannon