To reset tcpip in the registry
netsh int ip reset resetlog.txt

Windows 7, 8, 8.1, 10+
Techie version:
start
cmd
Control+Shift+Enter
run cmd as administrator
netsh winsock reset catalog
netsh int ip reset reset.log
reboot


Non-Techie step by step version:
Click the Windows Start button on the screen or on the keyboard
in the white box type the next information in there:
c:\windows\system32
find cmd and right click on it and run as administrator (You may have to answer yes to allow changes to windows)
A black and white screen will come up C:\ with a bunch of words. 
To the right of the > type the next line
netsh winsock reset catalog   (and press Enter) We don’t care about the results, just move on.
To the right of the > type the next line
netsh int ip reset reset.log   (and press Enter) We don’t care about the results, just move on.

Reboot the computer


Windows 2000
Boot to safe mode
Remove TCPIP
Reboot
Export Winsock and Winsock2 keys
Reinstall TCP/IP

Windows XP Home or Professional
Unable to Automatically obtain an IP Address or I get an IP Addess of 169.254.x.x and I know DHCP Server is running somewhere on the network
Start
Run
notepad c:\windows\inf\nettcpip.inf
Control H
Find 0xA0
Replace with 0x80
Replace All
Save and exit notepad
Control Panel
Network connections
Lan properties
Install
Protocol
Have disk
c:\windows\inf
TCP/IP (not tcpip v6)
Highlight Internet Protocol TCP/IP
Uninstall
Reboot
(After reboot) Start
Run
Regedit
My Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services (Not CurrentControlSet001 or 2 or 3)
Highlight Winsock
Delete key
Highlight Winsock2
Delete key
Close regedit
Control Panel
Network connections
Lan properties
Install
Protocol
Internet Protocol TCP/IP
Reboot
Fixed
When you are prompted to confirm the deletion, click Yes.