Hello, thanks for your answer, I succeed in restoring an old backup of the vm and made the site online again, lot of job since and that's why I made so long to answer you.
Here's the error message I had when, with the Proxmox web interface lost, I tried "qm start 101" :
Virtual Environment 5.1-51
Virtual Machine 101 (irc2018pmox2) on node 'xxxxxxxx'
Logs
()
kvm: -drive file=/var/lib/vz/images/101/vm-101-disk-2.qcow2,if=none,id=drive-sata0,format=qcow2,cache=none,aio=native,detect-zeroes=on: qcow2: Image is corrupt; cannot be opened read/write
TASK ERROR: start failed: command '/usr/bin/kvm -id 101 -name xxxxxxxxxx -chardev 'socket,id=qmp,path=/var/run/qemu-server/101.qmp,server,nowait' -mon 'chardev=qmp,mode=control' -pidfile /var/run/qemu-server/101.pid -daemonize -smbios 'type=1,uuid=dbed3870-a1be-4b39-a474-85d5c207e49d' -smp '2,sockets=1,cores=2,maxcpus=2' -nodefaults -boot 'menu=on,strict=on,reboot-timeout=1000,splash=/usr/share/qemu-server/bootsplash.jpg' -vga cirrus -vnc unix:/var/run/qemu-server/101.vnc,x509,password -cpu kvm64,+lahf_lm,+sep,enforce -m 8192 -device 'pci-bridge,id=pci.1,chassis_nr=1,bus=pci.0,addr=0x1e' -device 'piix3-usb-uhci,id=uhci,bus=pci.0,addr=0x1.0x2' -device 'usb-tablet,id=tablet,bus=uhci.0,port=1' -device 'virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3' -iscsi 'initiator-name=iqn.1993-08.org.debian:01:bb96ea23a5a' -drive 'if=none,id=drive-ide2,media=cdrom,aio=threads' -device 'ide-cd,bus=ide.1,unit=0,drive=drive-ide2,id=ide2,bootindex=200' -device 'ahci,id=ahci0,multifunction=on,bus=pci.0,addr=0x7' -drive 'file=/var/lib/vz/images/101/vm-101-disk-2.qcow2,if=none,id=drive-sata0,format=qcow2,cache=none,aio=native,detect-zeroes=on' -device 'ide-drive,bus=ahci0.0,drive=drive-sata0,id=sata0,bootindex=100' -netdev 'type=tap,id=net0,ifname=tap101i0,script=/var/lib/qemu-server/pve-bridge,downscript=/var/lib/qemu-server/pve-bridgedown,vhost=on' -device 'virtio-net-pci,mac=02:00:00:db:92:ee,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300'' failed: exit code 1"
The vm is started and online but I still do not have the Proxmox web interface online and I don't know if it can make the site down again if I try to reinstall Proxmox on the server ...
Thanks for your advises ,
Laurent