If you have resized the partitions, then that might have changed the partition table, so if the linux partition is still there, you might require to point to the correct partition in your file like fstab,grub/lilo.
To change these files, you need to access them, which can only be done by using an alternate boot device which can be
1. Rescue disk/floppy
2. Linux installed on some other partition, you need to boot using that.
3. Unplug this drive, plug into some system which has linux installed and boot this as secondary device, then mount the root partition and edit the required files.