When I install the window 7 in my pc then the pc said window cant install in local disk c?

Firstly, is there enough space on your C drive? 32 bit needs 16Gb & 64bit needs 20Gb just for its self, so if you have more than a single partion give C more space.

If the room is there, you could try formating the hard drive first. You can achieve this by performing a Windows 7 custom install, this will allow you to go to drive options ( advanced).

For a guide to W7 installation that may assist:-

www.sevenforums.com/tutorials/1649.clean-install-windows-7-a.html

This is not a full list of things to try but a starter to establish a sound base to work from.

Hope this of some help.