Windows 7 - Can't connect to wifi - driving me nuts!

Until yesterday morning I had a good wifi signal. We are in France and run on Nordnet Satellite Internet.
However, now I have an exclamation mark on signal bar and no internet access. We are on Nordnet Satellite and I am running WIndows 7 on a Sony Vaio laptop.
It is not the router as my husband's laptop is working fine with no connection problems. I can connect to internet by using cable but not wifi which is very inconvenient as I have to keep bringing the computer downstairs.
Have done diagnostic check and error is: Windows cannot connect with the device or resource (primary DNS server)
Computer also trying to connect by cellular profile (which is the O2 dongle that I use when I go to the UK). I keep getting the O2 box up asking me if I want to connect which it did (without the dongle inserted) but although it will bring up Google it won't connect to anything.
I'm not very technical but have done the obvious things like system restore and checking the adaptor settings in Network and Sharing but just can't figure out what the problem is. If I try to set up a new connection it just keeps referring back to the cellular profile which is presumably for O2?
Can anyone shed any light on this - would really appreciate any help!

Hello Sally, welcome to Windows Seven Forums.

Have a look at this possible solution: Can't communicate with Primary DNS Server - Microsoft Answers

Hi Sea Vixen (nice user name!)
Tried option 1 but on the 'fix it yourself' option I put in all the command prompts but it failed as says I am not administration (which I am).

Second option
Method 2.
Step 1.
1. Connect to your router (by typing 192.168.0.1 or 192.168.1.1 in the address bar) and log in. Check your user manual or documentation if you do not know the log-in credentials.
2. Make sure you are in the Setup -> Basic Setup category.
3. Scroll down until you see 'DHCP Server' - if it is disabled, select 'Enable'.
4. Enable DHCP If you want, you can change the number that the DHCP IP assigning starts. (this is optional)
5. Use the DNS servers provided to you by your ISP. There are many DNS servers out there. It's best to use your ISP's if possible.
6. Scroll down and click 'Save Settings'.

Tried to do this but not quite sure if I am doing it right as when I put the number into the address bar (which I assume is where the www web address goes) it just brought up a list of websites!

Can you tell me if I'm doing something wrong?

are you putting the numbers as in doing a google search? you want to put the numbers at the very top of the page up where the back arrows are if your using internet explorer 9. You will see http://www.severnforums.com etc etc in he address bar as you are looking at this forum page you need to type the ip address for the router in that area

Many laptops have a small switch or an Fn key touch to disable WiFi...

Have you accidentally disabled your WiFi adapter?

C'est tout à fait possible, non?

Check there's no arrow, exclamation mark, or triangle beside your WiFi adapter in Device Manager...

Do check Qdos's suggestions first, as we often forget the simple things when trying to help out.

Failing that, try option 1 again, but before you open the command prompt window, right-click cmd and choose Run as Adminstrator, which will give you full elevated privileges.