Windows 98 Lockup

Hi everyone, first post here, I have a question about Windows 98 running on a IBM Thinkpad 233 Pentium, first of all it’s not mine, it’s my uncles. The problem he has is that about after 15 minuites online, it totally freezes up, ctrl alt del doesn’t even work. We checked to see if it has any conflicts but everything seems to check out alright, it also locks up every once in a while while not online. ANY suggestions are greatly appriciated. Thanks