what i do when installing windows server is usually create a virtual floppy disk with -fda
try to start the vm, and then ssh to the host and enter the command
#ps ax | grep vmid
0:21 [kjournald]
2115 ? Sl 2276:31 /usr/bin/kvm -id 101 -chardev socket,id=qmp,path=/var/run/qemu-server/101.qmp,server,nowait -mon chardev=qmp,mode=control -vnc unix:/var/run/qemu-server/101.vnc,x509,password -pidfile /var/run/qemu-server/101.pid -daemonize -usbdevice tablet -name Debian-Proxy -smp sockets=1,cores=2 -nodefaults -boot menu=on -vga cirrus -k en-us -drive if=none,id=drive-ide2,media=cdrom,aio=native -device ide-cd,bus=ide.1,unit=0,drive=drive-ide2,id=ide2,bootindex=200 -drive file=/var/lib/vz2/images/101/vm-101-disk-1.raw,if=none,id=drive-virtio0,cache=directsync,aio=native -device virtio-blk-pci,drive=drive-virtio0,id=virtio0,bus=pci.0,addr=0xa,bootindex=100 -m 1729 -netdev type=tap,id=net0,ifname=tap101i0,script=/var/lib/qemu-server/pve-bridge,vhost=on -device virtio-net-pci,mac=0E:84:51:4B:31:BF,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300
stop the vm
and start again with -fda /path/to/virtio-drivers.vfd
root@proxmox#/usr/bin/kvm -id 101 -chardev socket,id=qmp,path=/var/run/qemu-server/101.qmp,server,nowait -mon chardev=qmp,mode=control -vnc unix:/var/run/qemu-server/101.vnc,x509,password -pidfile /var/run/qemu-server/101.pid -daemonize -usbdevice tablet -name Debian-Proxy -smp sockets=1,cores=2 -nodefaults -boot menu=on -vga cirrus -k en-us -drive if=none,id=drive-ide2,media=cdrom,aio=native -device ide-cd,bus=ide.1,unit=0,drive=drive-ide2,id=ide2,bootindex=200 -drive file=/var/lib/vz2/images/101/vm-101-disk-1.raw,if=none,id=drive-virtio0,cache=directsync,aio=native -device virtio-blk-pci,drive=drive-virtio0,id=virtio0,bus=pci.0,addr=0xa,bootindex=100 -m 1729 -netdev type=tap,id=net0,ifname=tap101i0,script=/var/lib/qemu-server/pve-bridge,vhost=on -device virtio-net-pci,mac=0E:84:51:4B:31:BF,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300 -fda /path/to/virtio-drivers.vfd
this things are obsolete, but might works
hth