I have similar problem, after i booted to windows, i can not boot the OpenSUSE.
The Grub menu is gone. All i can do is boot from DVD. Choose Installation or Rescue.
What should i do?, so I can come back using OpenSUSE and Windows 7.
You can repair using the installation DVD and just making boot from the DVD. Following the path following repairs: New Installation -> Update -> Repair Installed System
Choose repair and next to Repair Method. Select Expert tools. You will be presented (so it is best to express it) with Repair Tool Box screen. Choose to boot-break down (Boot installed system). If more than one plant in our hard disk will display a list of all the partition you have to choose where to boot-virtue, otherwise it will start automatically.
You might want to have a look at this post: Windows and openSuse 11.4 dual boot problem and try that first. I actually wonder if it works (don’t have Windows myself). You NEED to know which of the 4 partitions has Grub before doing that. If you activate the wong one, neither Windows nor Linux will boot. However this is easy to fix with fdisk on a Linux live system, as explained here Windows and openSuse 11.4 dual boot problem (of course the partition number may be different for you).
The two links refer to the same thread but to different posts.