[ubuntu] error: unknown filesystem. grub rescue>

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http://ubuntuforums.org – I'm an old guy and as much as I hate to admit it, I don't seem to be able to resolve problems when they occur any more. My laptop is a Acer Aspire 7711Z-4433 and I lost my wireless connection to my router. It came with Windows 7 and I have all of the disks. I reinstalled Windows but I now get an error message "unknown file system. grub rescue>". I really do enjoy ubuntu but when I have these type of problems they are beyond my ability to correct them. Can anyone tell me how to clear the afore mentioned error message or better yet how to format the hard drive. I cann (Hardware)