hi! intially i was having only windows on my system, i installed ubuntu and imported all the hard disk drives to ubuntu. Now windows got corrupted and are not running and i want to keep only ubuntu on my system. I can access the data of windows and partitions formatted by windows through ubuntu because i imported them but i cannot do changes like cut, paste, delete,copy etc. how should i remove windows so that i have full access on my harddisk

I would use Gparted in Ubuntu to Erase my Windows Partition. The trouble is you haven't stated whether you have a Wubi install of Ubuntu or a True Dual boot install.