You can do two things here with this......
1.) Reformate the HDD again but this time try to find a utility that will delete the Master Boot Record. To do this you will need a special peice of software. I found a site that has a free one available:
http://www.killdisk.com/downloadfree.htm I have not used it but it should work from what I read. This will delete the entire Hard Disk Drive!!!! back up everything. I refurbish PCs on the side for extra cash and resell them. I use a tool called Erase Disk that I paid for. It does the same thing.
2.) The other simpler but less clean option is to Right click on My Computer, go to properties, Select Advanced, Select Start Up and Recovery (Settings), Take the check out of Time To Display list of Operating Systems. CLick OK then OK again. You should not see that message when you reboot again.
Let me know if any of this is not clear and I need to elaborate more.