Download and use EasyBCD. It can do one or two usful things. In your case it can be used to restore the MBR so that you can dual boot. If you have any problems understanding how to use it, post back and someone on these pages will help you.
Operating System Windows 7 All varieties (64Bit) Now Windows 8
Computer Type Self built
CPU Type and Speed AMD X4 2.8 Ghz
Motherboard Chipset Gigabyte MA74GMT
System Memory Type 4096 MB DDR-3 1333 Mhz
Video Card Type and Speed Radeon HD 5450 1024 MB PCI-E
Hard Drive 320 GB SATA
Anti-virus Software MSE
Computer Skill Level Self-Taught Expert
Favorite Game Pool/snooker Online.