Gentlemen,
as you are all no doubt aware, when you start the machine, BIOS is loaded into the first 64K of RAM, and the BIOS then does a hardware check to ascertain what is connected to the motherboard. After this interrogation, Bios looks for the boot sequence, in the order set up in the BIOS. When it finds this info, it hands over control to the boot sequence (in this case WIN98's operating system), and WIN 98 then also does a check of the BIOS to see what hardware is connected, while also doing some checking of its own to find other things (CD ROMS, USB devices, etc). WIN 98 then loads the appropriate virtual device drivers to run these units, and then goes into the GUI desktop.
From my experience (in this field, considerable) the major cause of slow starts is hardware related (the system looking for bits)AND BIOS setup. Check the BIOS setup is correct as the first thing. Any hardware drivers changed or removed/added recently? Etc Etc...
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When all else fails, read the manual!