Unable to modify re-opened files in vim(file permissions not a problem)

I am working with vim. I created a new cpp file using

vim xyz.cpp

After opening the file, I added some basic includes and comments. Then I closed 开发者_JS百科it(:wq!) and re-opened it only to find that I am not able to delete/edit the previously written commands, even after pressing i (for insert), although it gets into insert mode and I am able to add new text to the file. I must say that when i am NOT in the insert mode, then I am able to delete individual characters by pressing x . But it doesnt solve my problem.

I checked the file permissions and it says -rwxrwxrwx, so I dont think permissions is the issue. Has anyone faced this problem before. Any kind of help will be appreciated.

Thanks

:help 'backspace' is your friend

    Influences the working of <BS>, <Del>, CTRL-W and CTRL-U in Insert
    mode.  This is a list of items, separated by commas.  Each item allows
    a way to backspace over something:
    value   effect  ~                               
    indent  allow backspacing over autoindent
    eol     allow backspacing over line breaks (join lines)
    start   allow backspacing over the start of insert; CTRL-W and CTRL-U
            stop once at the start of insert.

    When the value is empty, Vi compatible backspacing is used.

Try to set it to

 set backspace=indent,eol,start