thanks for the replies guys, so i just tried changing the MTU size and also renewing DHCP lease.
I have ensured the wifi is on.
have 'added' a network.
We have around 20 people in this community so there are like 18 laptops and they have no issues with the wifi which is why i didn't bother turning the router on and off again. but I've turned the laptop on and off again!
hmm its very confusing.. still no luck
You can try running the Apple Hardware test, but it isn't 100% reliable.
If you live near an Apple Store, make a Genius Bar appointment to have the computer tested. Supposedly there is no charge for testing. You may have a Wi-Fi card problem.
First contact your ISP. You need to confirm that the issue is not on their end.
Change your router channel. Sometimes this is all you will have to do.
Power cycling the router. Read the router's user manual or contact their tech support for instructions.
System Preferences/Internet & Network/Network
Unlock the padlock
Click the Assist Me button
In the popup window click the Diagnostic button.
System Preferences/Network- Unlock padlock. Highlight Airport. Network Name-select your name. Click on the Advanced button. Airport/Preferred Networks-delete all that is not your network.
Place a check mark next to "Remember networks this computer has joined." Click the OK button and lock the padlock. Restart your computer.
http://support.apple.com/kb/TS1920 Mac OS: How to release and renew a DHCP lease
No internet connection (wireless)
Check to see if an extra entry is present in the DNS Tab for your wireless connection (System Preferences/Network/Airport/Advanced/DNS).
Delete all extra entries that you find.
Place a check mark next to "Remember networks this computer has joined."
Other resources to check into:
If using one of Apple's Airport routers, read its user manual or post in its forum area. If using a 3rd party router, read its user manual, contact their tech support department/website or post in its forum area. Another possible solution - read mammothsuziq response https://discussions.apple.com/message/22082360#22082360