Having problem with 1 pc on my wireless network

Hi,
I have 3 pcs sharing a wireless connection.
Pc 1 is running Windows XP Pro and is connected to the router.
Pc 2 is running Windows 98 and uses a wireless adapter.
Pc 3 is running Windows XP home and uses a wireless adapter. This is the Pc that I am having the problems connecting and staying connected to the internet. This pc is a Sony Vaio Pcvrz32g. I cannot stay connected to the internet with this pc. I must restart my Vaio and then reset the modem and router a couple of times a day just to get back on. It blinks out for no reason. If pc2 access the internet the Vaio will not be able to stay online. All the pages just time out. The adapter always says the strength is good but you can't connect to any pages. I tried to set the Wep encryption last night and all the pcs could access the internet except the Vaio.

What is wrong with this one pc?
I wanted to buy a new router because mine is so old and doesn't have the speed or security of the newer models but there is no point until I can figure out what is happening with this one pc.

Thank You for any help you can give.