MODX Revolution 2.2.1-pl (traditional) problem to see Url suddenly

Dear,
I am new bi here, so if the post in different area then accept my apology. The fact is my wesite was built by using MODX Revolution 2.2.1-pl (traditional) . Recently I am facing a problem that is: I can see my first page of the website but while I click any link the it shows "The requested URL /xxxx/xxxxx was not found on this server" whether it was ok and I can log on to Manager panel and there I see the page and content is there.
Can anybody help me regarding that fact please?