Now a day, I usually get disconnected but the two small comuters (the connection icon) still remains on my taskbar and even if I try to disconnect it, it does't work. When I try to connect again, it says that your modem is already in use. Every time this problem occurs, I have to restart my computer to go online again.

I am using Win XP.
I have AVG, McAfee, AdAware and Ewido Anti Spyware Installed and updated.

Please help me.

GB

Sounds like you have a rogue dial hijacking your connection.
Best advice would be to seriously scan your system, both for viruses and Spyware.
I see you already have adaware and ewido, Spybot (http://www.spybot.info/) is also worth trying.
When scanning its best to do it in Normal and Safe moe to ensure everything is removed.

Before you start scanning make sure you've cleared your internet cache (history, temp files and cookies) makes the scan run faster.
A good little program that can help with this is CCleaner (http://www.ccleaner.com) also helps to remove any junk files and does a good job of cleaning your registry too.

Good luck

Another possibility is that something is causing you to lose your connection, either noise on the line, someone picking up an extension, a problem on the ISPs end, etc. When this happens, the modem is not being reset to be able to dial again. What you would need to do is send a hangup code to the modem.

How to do so depends on what modem you have.

Frankly, I would recommend getting broadband.