Put your Windows 7 disc into the drive,when the pc is loading up press F12 to open boot options>boot from the dvd drive.
When you get into the Windows 7 disc>click repair>Select yourwin7 os>next>Run start up repair x3 (it sometimes take more than one attempt.)
If that does not work,go back into the repair console and enter the command promt section and type bootrec /fixmbr
This should try fixing the boot loader,and then you can select which OS to boot into.
Also can you download Partiton Wizard Boot dosc from another PC and burn it. Free Download Partition Wizard
Boot from this>select 1 for resolution>OK to the warnings.
Then have a look at your disc management.
Both partitons should be set as primary and active and NTFS.
If you change any of the options using partiton wizard make sure you click apply after each change.