General :: Can't Boot After Empty Primary Partition Was Made Unallocated

On a certain computer, I had four primary partitions. The person who installed the Windows 7 on the computer made two partitions for the Windows (sda1 and sda2). Then I made another two primary partitions (sda3 and sda4). sda3 was empty. sda4 is an extended partition that contained the /swap, and /.According to someone else, some viruses get in on the Windows partitions and can then get over to the Linux partitions if they are primary and right after the Windows partitions, or something like that. This person suggested that I create sda3 when I install Linux(SLES 10), but to install Linux on sda4. Then later I can change sda3 to secondary.So I tried this, and the Linux installation went fine.

I decided to change sda3 before I load the application software onto the computer.So I put the GParted CD in, but to my surprise I realised that the harddisk was actually 1 TB, and not 500 GB as I thought. So I had extra space to the right of sda4. I wasn't quite sure what to do with sda3. I thought that perhaps it would be better to unallocate sda3, move the current sda4 to the left, and then make another primary partition on the right of sda4, or just stretch sda4 both ways.Anycase, I unallocated sda3, and just left sda4 as it was.Hm, perhaps you can anticipate the end of the story. I removed the GParted CD, and restarted the computer, but now the computer doesn't let me choose whether I want to boot into Linux or Windows. Um, it doesn't boot at all from the harddisk.

I know it's dangerous to play with partitions, but sometimes the job won't be done if you are too afraid of doing anything, and I dare say you won't learn anything either. There was nothing on sda3, so I didn't think it would have nasty after effects. There isn't any important data on this computer yet, it was two new installations of Windows and Linux. So I guess I could format the harddisk and just reinstall everything, but I would like to learn what goes on underneath the surface.