lucy24 - 8:13 pm on Aug 29, 2012 (gmt 0)

I checked after a a couple of hours and when I typed www.example.com I am redirected to http://www.example.com/cgi-sys/defaultwebpage.cgi for some unknown reason for me

Do you mean that your address bar changes? What is the content of the page you end up at? It looks like the default starter page for some CMS-- in other words, not necessarily a mistake.

but when i type http://www.example.com/~account_name/ my website is shown.

Again, does the address bar change?

It sounds as if something got mixed up when you were updating the DNS information, assuming that's what you meant by "changed in my domain registrant". And assuming you really meant "changed IN", not simply "changed".

First step: test with a tool such as Firefox LiveHeaders. (Other browsers probably have equivalents by now.) This will show you exactly what is happening.

Also: look at your raw logs. Each redirect will be visible as a 301. Unfortunately the logs will not say what the redirect points to-- but if it is a human visitor (including yourself) the 301 will be followed by a fresh request for a different URL. Browsers go where they are told to go.

It's no use asking what to do until everyone knows exactly what's happening right now. Otherwise you risk creating an even bigger mess.