You have linux and windows on your hdd,
As it happened you needed to reinstall M$ Windows, after that operation your GRUB is not visible after reboot.
Resolution:
1. run any of the Linux LiveCD distros (I used Ubuntu)
2. in Console type (as root or sudo):
-> grub
3. in Grub app (I had my linux partition on /dev/sda7 which is mapped to hd0,6 in GRUB):
-> root (hd0,6)
-> setup (hd0,6)
4. reboot
5. you're done if everything went fine -> I hope so :)
thanks,
chris