uninstalling ubuntu 14.04
 

I wanted to uninstall ubuntu from my dell laptop on which i have windows 8 running alongside, so i deleted the partition n expanded my drive c and when i restarted the laptop i got this error message:
error: no such partition.
Entering rescue mode...
grub rescue>
I also tried booting frm my usb device and it gave this error message:
An operating system wasn't found. Try disconnecting any drive that don't contain an operating system.
Press Ctrl+Alt+Del to restart
And the message keeps repeating the same thing
Pls how do i go about this

If you had both installed using mbr, then you appear to have the Ubuntu Grub bootloader installed there pointing to the Ubuntu partition which is where almost all the boot files/code needed to boot resides. You should have installed the windows code to the mbr. You will probably need a windows installation disk to repair though a Recovery CD may do it.

If you were using efi for windows 8 and Ubuntu, it's a different setup but you haven't indicated which you are using.

reinstall the Microsoft bootloader
the one you overwrote with grub

use the windows rescue dvd you made the VERY first time you turned on the computer
( you were instructed to MAKE a rescue dvd )

or
get one from microsoft

I too would be interested to know if your system is mbr or uefi.