Thats wierd lol. If your able to come here and post that you can't ping anything then you should be able to ping things!!! Van help the man dammit!  

1.Have you tried disabling your firewall.
2.Has your ISP disabled the ability for you to ping.  (Many are moving that way).  Change the last number of your IP Address to one.  If you can ping it the "problem is not in your set"
3.Is your HOSTS file intact?
4.Check your C:\windows\system32 for the hosts file. On mine (XP Pro) it's in the  C:\windows\system32\drivers\etc.  Or just search for it in the windows dir through windows search...
5. Can you tracert?  How about a netstat (working)?
6. You may have a HOSTS "hijack" on your system.  Run SpyBot Search & Destroy (free) to check for that and hundreds of other nasties out there.  I love it!  Nobody should be without SpyBot.   Nobody!
7. Your TCP/IP software may  not be setup quite correctly, or your Winsock could be damaged.

You can get excellent assistance for these things at another forum that I often work at (au gratis).  They'll have you get a copy of HiJackThis!, and then use the log it creates to diagnose your system ...usually in just a few minutes tops.  
http://forums.net-integration.net   or
http://wildersecurity.com  or MAYBE (sometimes) there is info to be had at
http://maddoktor2.com  (though it can get 'strange' in there.  

I wish you the best as there are several other variables that could cause your PC to go "pingless"  ....including the need to reload your O/S.  (last ditch effort there).

Cheers,

The Reverend

I found a solution that worked for me.
Some server monitoring software I tried out (BixData) seemed to cause my problem.

By removing the following registry item I could instantly ping again:-

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Parameters\DefaultTTL