I found this article by Googling "Can't enable msconfig in IE7"
Go Here: http://www.raymond.cc/blog/archives/2008/0...at-run-command/
I suspect there is more to this than just solving the "msconfig" but go ahead and read this article and hopefully someone with more expertise than me will come along and help.
Here is an additional possibility. See if you can find IE7 in "start>control panel>add and remove programs" and try and uninstall it and then attempt to re-install it and see if it works then.
you may need to uninstall IE8 & IE7 first which should leave you with IE6. See if that is working properly for you and go from there. If IE6 is running ok then it may be that you have some corrupted files in IE7 and/or IE8. If IE6 won't let you go to updates or connect you to the internet then I would probably start to look for some type of infection.
Hope this article gives you some enlightenment.