How do troubleshoot JAVA

Hey gang....

Have a few clients that are using websites with JAVA embedded to do thier day to day work...most of the machines work no problem...

Have one machine that was Win98 client could log on but when she did anything it would hang up the box....we upgraded it to XP even though another 98 machine works fine...and still no luck

Another machine ...client loggs on fine but the page will come up done with nothing on it or will hang the box. I tried downloading sun Java and it work for two weeks...it would prompt her for a certificate ...you would click ok...now it is broke ...it doesnt prompt for anything and even uninstalling and reinstalling dont work...


Any ideas on how to troubleshoot....JAVA