Windows 7 Installed along with Windows XP does not work

Laptop Configurations:
- HDD- 580 GB
- RAM – 2 GB
- Graphic card – Nvidia
- Processor – Inter core 2 duo
I had Windows 7 ultimate 32 bit installed on my laptop but one of my favorite game total overdose wasn't working in it, that's why I decided to install Windows XP with service pack3 without removing Windows 7 thinking that both OS can work together.
Windows XP installed successfully but then I couldn't run Windows 7 on my laptop. I tried running Windows 7 startup repair but no luck. Then I formatted the drive in which the Windows XP was installed, still Windows 7 is not running. Now I re-installed my Windows XP with service pack 3 and I am stuck with this only. Please suggest a way to get back my Windows 7 back as it was before installing Windows 7.
