Bonjour et merci pour votre aide.
Pour répondre voici ce que donnent les commandes indiquées par tlep:
[root@colline eric]# cat /proc/bus/usb/devices
T: Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2
B: Alloc= 93/900 us (10%), #Int= 1, #Iso= 0
D: Ver= 1.10 Cls=09(hub ) Sub=00 Prot=00 MxPS=64 #Cfgs= 1
P: Vendor=0000 ProdID=0000 Rev= 2.06
S: Manufacturer=Linux 2.6.17-5mdv uhci_hcd
S: Product=UHCI Host Controller
S: SerialNumber=0000:00:04.2
C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr= 0mA
I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
E: Ad=81(I) Atr=03(Int.) MxPS= 2 Ivl=255ms
T: Bus=01 Lev=01 Prnt=01 Port=01 Cnt=01 Dev#= 3 Spd=1.5 MxCh= 0
D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
P: Vendor=045e ProdID=0039 Rev= 1.21
S: Manufacturer=Microsoft
S: Product=Microsoft IntelliMouse® Optical
C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA
I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=01 Prot=02 Driver=usbhid
E: Ad=81(I) Atr=03(Int.) MxPS= 4 Ivl=10ms
[root@colline eric]# tail -f /var/log/syslog
Mar 7 13:42:10 localhost scsi_id[4407]: scsi_id: unable to access '/block/sda'
Mar 7 13:42:10 localhost scsi_id[4408]: scsi_id: unable to access '/block/sda'
Mar 7 13:42:11 localhost kernel: usb 1-1: device not accepting address 19, error -71
Mar 7 13:42:11 localhost kernel: usb 1-1: new full speed USB device using uhci_hcd and address 20
Mar 7 13:42:11 localhost kernel: usb 1-1: device not accepting address 20, error -71
Mar 7 13:42:11 localhost kernel: usb 1-1: new full speed USB device using uhci_hcd and address 21
Mar 7 13:42:11 localhost kernel: usb 1-1: device descriptor read/64, error -71
Mar 7 13:42:12 localhost kernel: usb 1-1: device descriptor read/64, error -71
Mar 7 13:42:12 localhost kernel: usb 1-1: new full speed USB device using uhci_hcd and address 22
Mar 7 13:42:12 localhost kernel: usb 1-1: device descriptor read/64, error -71
Mar 7 13:42:12 localhost kernel: usb 1-1: device descriptor read/64, error -71
Mar 7 13:46:22 localhost kernel: usb 1-1: new full speed USB device using uhci_hcd and address 23
Mar 7 13:46:22 localhost kernel: usb 1-1: configuration #1 chosen from 1 choice
Mar 7 13:46:22 localhost kernel: scsi5 : SCSI emulation for USB Mass Storage devices
Mar 7 13:46:22 localhost kernel: usb-storage: device found at 23
Mar 7 13:46:22 localhost kernel: usb-storage: waiting for device to settle before scanning
Mar 7 13:46:27 localhost kernel: Vendor: Sandisk0 Model: ImageMate SDDR09 Rev: 0100
Mar 7 13:46:27 localhost kernel: Type: Direct-Access ANSI SCSI revision: 00
Mar 7 13:46:27 localhost kernel: usb 1-1: reset full speed USB device using uhci_hcd and address 23
Mar 7 13:46:27 localhost kernel: usb 1-1: device not accepting address 23, error -32
Mar 7 13:46:28 localhost kernel: usb 1-1: reset full speed USB device using uhci_hcd and address 23
Mar 7 13:46:28 localhost kernel: usb 1-1: device not accepting address 23, error -32
Mar 7 13:46:28 localhost kernel: usb 1-1: reset full speed USB device using uhci_hcd and address 23
Mar 7 13:46:28 localhost kernel: usb 1-1: device descriptor read/64, error -32
Mar 7 13:46:28 localhost kernel: usb 1-1: device descriptor read/64, error -32
Mar 7 13:46:29 localhost kernel: usb 1-1: reset full speed USB device using uhci_hcd and address 23
Mar 7 13:46:29 localhost kernel: usb 1-1: device descriptor read/64, error -32
Mar 7 13:46:29 localhost kernel: usb 1-1: device descriptor read/64, error -32
Mar 7 13:46:29 localhost kernel: usb 1-1: USB disconnect, address 23
Mar 7 13:46:29 localhost kernel: sda : READ CAPACITY failed.
Mar 7 13:46:29 localhost kernel: sda : status=0, message=00, host=1, driver=00
Mar 7 13:46:29 localhost kernel: sda : sense not available.
Mar 7 13:46:29 localhost kernel: sda: Write Protect is off
Mar 7 13:46:29 localhost kernel: sda: Mode Sense: 00 00 00 00
Mar 7 13:46:29 localhost kernel: sda: assuming drive cache: write through
Mar 7 13:46:29 localhost kernel: sda : READ CAPACITY failed.
Mar 7 13:46:29 localhost kernel: sda : status=0, message=00, host=1, driver=00
Mar 7 13:46:29 localhost kernel: sda : sense not available.
Mar 7 13:46:29 localhost kernel: sda: Write Protect is off
Mar 7 13:46:29 localhost kernel: sda: Mode Sense: 00 00 00 00
Mar 7 13:46:29 localhost kernel: sda: assuming drive cache: write through
Mar 7 13:46:29 localhost kernel: sda : READ CAPACITY failed.
Mar 7 13:46:29 localhost kernel: sda : status=0, message=00, host=1, driver=00
Mar 7 13:46:29 localhost kernel: sda : sense not available.
Mar 7 13:46:29 localhost kernel: sda: Write Protect is off
Mar 7 13:46:29 localhost kernel: sda: Mode Sense: 00 00 00 00
Mar 7 13:46:29 localhost kernel: sda: assuming drive cache: write through
Mar 7 13:46:29 localhost kernel: sda:<3>Buffer I/O error on device sda, logical block 0
Mar 7 13:46:29 localhost kernel: Buffer I/O error on device sda, logical block 0
Mar 7 13:46:29 localhost kernel: Buffer I/O error on device sda, logical block 0
Mar 7 13:46:29 localhost kernel: unable to read partition table
Mar 7 13:46:29 localhost kernel: sd 5:0:0:0: Attached scsi removable disk sda
Mar 7 13:46:29 localhost kernel: sd 5:0:0:0: Attached scsi generic sg0 type 0
Mar 7 13:46:29 localhost kernel: usb-storage: device scan complete
Mar 7 13:46:29 localhost kernel: usb 1-1: new full speed USB device using uhci_hcd and address 24
Mar 7 13:46:29 localhost usb_id[5232]: usb_id: unable to access '/block/sda'
Mar 7 13:46:29 localhost scsi_id[5234]: scsi_id: unable to access '/block/sda'
Mar 7 13:46:29 localhost scsi_id[5236]: scsi_id: unable to access '/block/sda'
Mar 7 13:46:30 localhost kernel: usb 1-1: device not accepting address 24, error -71
Mar 7 13:46:30 localhost kernel: usb 1-1: new full speed USB device using uhci_hcd and address 25
Mar 7 13:46:30 localhost kernel: usb 1-1: device not accepting address 25, error -71
Mar 7 13:46:30 localhost kernel: usb 1-1: new full speed USB device using uhci_hcd and address 26
Mar 7 13:46:30 localhost kernel: usb 1-1: device descriptor read/64, error -71
Mar 7 13:46:31 localhost kernel: usb 1-1: device descriptor read/64, error -71
Mar 7 13:46:31 localhost kernel: usb 1-1: new full speed USB device using uhci_hcd and address 27
Mar 7 13:46:31 localhost kernel: usb 1-1: device descriptor read/64, error -71