This kind of behaviour can be caused if the file scsi1hlp.vxd has been replaced by an incompatible one. have a look in C:\WINDOWS\SYSTEM\IOSUBSYS for scsi1hlp.vxd. Right click on the file and select "Properties". My version of this file is shown as version 4.10.1998, it is size 18.8KB (19,270 bytes), 24,576 bytes used.
If your file has changed, replace it with the original extracted from the Windows 98se cd using SFC.