cannot go online

I have not been able to go online on my PC though my colleague in the same office is able to. My default browser, Fire fox cannot connect and Internet Explorer also cannot connect. What can be wrong and what must I do to deal with it? I'm now using my laptop with a wireless connection.

How is the pc connected to modem or router? Wireless or wired?

Did you make ANY type of change to the pc?

artkaye--
Any error messages? Can you (just to test) move your PC to your colleague's office and see if it connects to the internet from there?
Is this something new? Try a System Restore to a date before the problem started.
But until we know the versions of Windows and IE you are using it is hard to make more specific suggestions.
A possible quick fix--try the following
"To resolve this problem in Internet Explorer, follow these steps:
Quit all programs that are running.
Click Start, and then click Run.
Type regsvr32 urlmon.dll, and then click OK.
When you receive the "DllRegisterServer in urlmon.dll succeeded" message, click OK.
(If this does not resolve the problem, repeat-- replacing Urlmon.dll with each of the file names below):
Shdocvw.dll
Actxprxy.dll
Oleaut32.dll
Mshtml.dll
Browseui.dll
Shell32.dll "
Don't worry if you get a message saying some of these actions are not successful.