Before re-installing, you should check whether your linux partitions are still fine or not. Boot from the rescue prompt and try to mount your linux root partition.
If it works, check the partition table using fdisk -l /dev/hda .
If you run pmagic in windews, check if it shows available ext2 or ext3 and a swap partition.
If it shows free space or unknown, you need a re-install. windews has messed your other partitions.
Also try entering the grub commands (root ***, kernel ***, initrd ***, boot) manually and check for the errors. Directions are given on the boot screen in grub.
To see the commands sequence, press 'e'. Note them down and enter them one by one.