You should select Install Ubuntu alongside other systems (Windows in your case) when presented with Preparing to installation dialogue box during Ubuntu installation.
- If you have chosen this option during install, give a try to boot-repair tool to fix your Grub entries.
If you have selected erase disk and install Ubuntu instead, I am afraid you may have lost your Windows installation already, with only Ubuntu present on your PC now.
Refer to this answer to get more information.
Since you say that you have selected Install Ubuntu alongside other systems, looks like you may be facing the RAID problem as mentioned here. I am outlining their solution to this problem here too -
Ubuntu seems to have marked one or more of your partitions as RAID.
- To fix it first turn off RAID in your bios.
- Then load up Ubuntu from liveDVD / liveUSB and open gparted. If you get a drive with a funny name like nvidia_ahahdhjdfsjkf then you have mounted a RAID drive that you don't want.
To get rid of it, Open a terminal and run:
$ sudo dmraid -E -r /dev/name_of_your_disk
- Note : you want the disk name not the partition name. You can see your disk names in gparted. e.g. if disk names are sda and sdb and partition names are sda1, sda5 and sdb1, then you have to do both sda and sdb.
Restart gparted. Once you have erased the RAID meta data you should see the funny named disk disappear.
- Once you have verified the RAID disk is gone reboot and your Windows OS should boot.
Source : Ubuntu Forums - Ubuntu has forced sda into a RAID
