If it WAS working ok in the dual boot configuration, I suggest you boot to 98 and see if you can run virus and malware scans at all. Try booting it in safe mode in Win98 by pressing the F8 key right after you select the boot from 98 menu option. You may get more control of your machine that way. For information on Malware removal visit the Security forum on this website and read the posts at the top of the page. You could have Malware running and active in the Windows98 system that is not present and active when the XP system is running.