Can you test the flash drive on another computer to see if it'll boot elsewhere, some old flash drives couldn't be used as boot..
Quick step by step. But I have an advantage of having a CD ROM.
Step 1. Was to set up the flash drive with DOS 7. Copy over the windows install file folder.
Step 2. Use the flash drive to create the partition. You'll not be able the activate the system boot partition, as the flash drive acts as a hard drive and DOS will not allow you to setup a second active partition.
Step 3. Reboot on the flash drive, format the partition, create the folder to contain the installation files eg. MD win98, copy over all the files from the windows install file to the folder.
Step 4. Reboot to CD ROM windows disk, to command prompt without CD ROM Support (No USB Drivers present so CD Rom wont be available). This acts as a virtual floppy/RAM drive, change over to c:\ drive, change to the win98 folder and run setup, follow directions from there.
Without CD ROM, you need to find a way to boot to some sort of virtual floppy drive. Try checking https://www.raymond.cc/blog/how-to-make-a-usb … drive-bootable/
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Windows 7 - HP730 Air cooled, 8Gb, GT1030
Windows 98se - Wyse V10LE 1.2Ghz, 1 Gb, 16Gb SSD
Windows 98se - Compaq Evo 550d SSF, P4 2Ghz, 1Gb, 60Gb(Partitioned)
Dos 6.2 - HP7510 512Mb, 4Gb