'ipconfig' is not recognized as an internal or external command, . . .

That's OK...such things happen Most important :you got it working !


So how could that have happened.....some reasons I could think of:
Malware,
3rd party applications to stream line/optimize Windows (which was fine for XP but should be avoided in se7en )
Some application that tried to add itself to the path variable but failed miserably...corrupting the former content in the process.
A hard shutdown due to a hung computer during a write operation.
A flipping bit on the harddrive due to a weak spot the magnetizing.
The RAM content got corrupted somehow and escaped the plausibility check while being written back.
(the last two virtually never happen or you would see other weird behavior)

-DG

You're very welcome, churin
Glad you got it figured out
For my taste way too many application feel the need to add themselves to the path (besides filling the registry with heaps of ***) That's why I usually set a restore point before any installation...reversing the whole process when something goes wrong.

Single Click Restore Point - - CNET Download.com

-DG

On one machine I just looked over where the owner had just closed out FaceBook and a new window suddenly opened he was unable to get online again when the malware bugged the registry as well as restore points. The network adapter driver was reinstalled and there was plenty of connectivity but not even adding a second browser could get him online.

Two restore points before that day were found useless as I expected when recommending a total wipe of the drive to start over. He's back on now. Goes to show that you can't always count on restore points.

One thing to consider trying would be the system file checker just to see if the tool will find the file corrupted and replace it. Simply type the sfc /scannow command in at the Start>Run to see if that will help. The other thought before an upgrade to repair or fresh install would be finding a way to manually expand the file from the 7 dvd.