I decided to delete ubuntu and change to ubuntu 12.04 as 14.04 does not have much softwares..
First, this is a mistaken assumption. I haven't checked the package manifests of the two versions of Ubuntu, but I'd be surprised if less was available for 14.04 than for 12.04. There's a lot of software available for Ubuntu (and for Linux generally). If you need a specific type of program and can't find it, post a question about that rather than do something radical (more radical than you realize; see below....).
I opened Disk Management and deleted two partitions which were unnamed(so they belonged to Ubuntu).(Three of the local disks changed to dynamic)
If attempting to downgrade from 14.04 to 12.04 was your first mistake, using the Windows Disk Management tool was the second one. You've identified the reason: That tool changed, without asking you, your disk from a standard partitioning setup to one that uses Logical Disk Management (LDM), aka dynamic disks. The trouble is that Ubuntu can't install to a disk that uses LDM, so by doing this, you've created a new hurdle for yourself.
There are lots of questions here that address this issue, such as:
The good news is that you can convert back, but you'll need to use third-party tools to do so -- see the earlier questions for links.
In the future, do not use the Windows Disk Management tool to do anything but shrink your Windows partition. It's got numerous known bugs that Microsoft refuses to fix and it tends to pull stunts like this one. Instead, use GParted,
gdisk, or other Linux tools; or perhaps third-party Windows tools (with which I'm relatively unfamiliar) for disk partitioning. Shrinking the Windows partition is a possible exception to this rule, since it's likely to be a little safer to use Microsoft's tool for this task. If you do that, though, do not create additional partitions in the free space; leave that task to the Linux installer or do it manually with a Linux program.
Once you've fixed your LDM problem, re-install 14.04. That will install a fresh copy of GRUB, which should work.
Incidentally, the problem with the
grub rescue> prompt is caused by the way GRUB works. Specifically, GRUB relies on files in the Linux partition, so as soon as you deleted the Linux partition, GRUB could no longer work properly -- but as the way you deleted Linux left GRUB in control of the MBR, GRUB still tried to work. If you wanted to delete Linux and continue using Windows, you'd need to re-install the Windows boot loader to the MBR, which you'd do either with a Windows recovery tool or by restoring a backup (if you'd had the expertise and foresight to create one; most people don't).