Had the same problem, the modem is not retro compatible, and therefore will not be recognised.
Not sure why you didn't up grade rather than downgrade, XP is about £80 to upgrade, but if you like to tinker, XP is not for you
OnePlus 5T review: Hands-on
Illustrator Andrés Lozano on his improv line work, brazen use of colours & hand sketching
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Comment envoyer gratuitement des gros fichiers ?