I have a problem with my wired connection. To be more specific, my laptop doesn't seems to recognize that I have plugged in an ethernet cable.

I tried to download new drivers for my ethernet card, but I couldn't find any solutions. Maybe because I am new to Linux, so I'm not familiar with running commands in the terminal.

OK I have typed the command and here are the results:

00:04.0 Ethernet controller [0200]: Silicon Integrated Systems [SiS] 191 Gigabit Ethernet Adapter [1039:0191] (rev 02)

For the second reply I don't know if the following is what you asked me:
?Memory: 3.9 GiB
?Processor: Intel Core 2 Duo CPU P8800 @ 2.66GHz × 2
?OS type: 32-bit

My Ethernet connection had some problem on Windows too. I have changed recently my internet provider, and since then my ethernet cable is not recognized by the laptop. At that time I was still on Windows. I thought that with Ubuntu the problem would be solved, but unfortunately the problem still persists. If someone can help me to solve my problem I'll be thankful.

Here are the results of the three first commands you told me to run:

lsmod | grep sis190 
sis190                 22570  0

sudo modprobe sis190

ifconfig 
eth0      Link encap:Ethernet  HWaddr 00:90:f5:90:81:7e  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:185 errors:0 dropped:0 overruns:0 frame:0
          TX packets:185 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:22672 (22.6 KB)  TX bytes:22672 (22.6 KB)

wlan0     Link encap:Ethernet  HWaddr 00:25:d3:2c:3a:ae  
          inet addr:192.168.1.72  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::225:d3ff:fe2c:3aae/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:260 errors:0 dropped:0 overruns:0 frame:0
          TX packets:363 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:71992 (71.9 KB)  TX bytes:52000 (52.0 KB)

and the results of running the last two commands:

dmesg | grep -e eth -e sis190 
[    0.816667] sis190: sis190 Gigabit Ethernet driver 1.4 loaded 
[    0.816728] sis190 0000:00:04.0: setting latency timer to 64 
[    0.816751] sis190: 0000:00:04.0: Read MAC address from EEPROM 
[    0.904032] sis190: 0000:00:04.0: Realtek PHY RTL8201 transceiver at address      
[    1.416030] sis190: 0000:00:04.0: Using transceiver at address 1 as default 
[    1.448235] sis190 0000:00:04.0: eth0: 0000:00:04.0: SiS 191 PCI Gigabit Ethernet adapter at f8410000 (IRQ: 19), 00:90:f5:90:81:7e 
[    1.448238] sis190 0000:00:04.0: eth0: GMII mode. 
[    1.448243] sis190 0000:00:04.0: eth0: Enabling Auto-negotiation 
[   11.560907] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready 
[   16.372019] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready 
[   16.372265] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready 
[   26.424038] sis190 0000:00:04.0: eth0: auto-negotiating...

nm-tool

NetworkManager Tool

State: connected (global)

- Device: eth0 -----------------------------------------------------------------   Type:              Wired   Driver:            sis190   State:         
unavailable   Default:           no   HW Address:       
00:90:F5:90:81:7E

  Capabilities:
    Carrier Detect:  yes

  Wired Properties
    Carrier:         off