If you can see your partitions you should be able to delete them now, if you do not need the data anymore.
-Delete all partitions.
-create new partitions
-install your OS
-say thank you Linux community for helping me reinstalling my Windows
-return here and ask us how to reinstall your Linux and youŽll be out of trouble
a little hint:
much more easier to use than fdisk is to get a life-cd like Knoppix or something like that ( i guess any bootable Linux-CD can do it ), boot it, switch to a console and type cfdisk
Easy little tool for partitioning