If it is a HP Laptop, it already has the maximum 4 partitions allowed, so you cannot create another partition with damaging one or more of the other 4, which you have discovered. So you cannot do what you want, use an external usb hard drive to store your data.
HP uses a custom Master Boot Record, using a recovery or regular Windows disc to fix the MBR will break this custom MBR, then your factory restore partition will not work.
HP has no easy method to repair the custom MBR other than do a full restore from the restore partition or HP recovery media. So back up your data and do a HP recovery.
I suggest you make your HP recovery media asap, label them appropriately and store in a safe place.
http://support.hp.com/us-en/document/c01867124?jumpid=reg_r1002_usen_c-001_title_r0001
Also make this disc
http://h20564.www2.hp.com/hpsc/doc/public/display?docId=emr_na-c02058933&DocLang=en&docLocale=en_US&jumpid=reg_r1002_usen_c-001_title_r0001
If you did not make your recovery media and cannot boot the PC:
You may be able to find HP recovery discs here since HP no longer offers them.
http://www.computersurgeons.com/Default.aspx
Also see this but W7 recovery media is no longer available from HP.
http://support.hp.com/us-en/document/bph07143
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