I had the same problem but all of the malware forum google results did not have an answer, so thought I would share and hopefully help others. I fixed it by:
Reboot into the Microsoft Windows Recovery Console, then (where D:\ is the Windows install CD-ROM or Service Pack);
expand d:\i386\ipsec.sy_ c:\Windows\system32\drivers\ipsec.sys
expand D:\i386\dnsapi.dl_ C:\Windows\system32\dnsapi.dll
expand D:\i386\dnsrslvr.dl_ C:\Windows\system32\dnsrslvr.dll
More info can be found at http://www.osisecurity.com.au/blog/zeroaccess-rootkit-sirefef-no-internet-connectivity-dns
... but it worked for me without repairing or reinstalling Windows. I'd be interested to hear if this helps anyone else.