I am trying to install mountain lion and when i press install it say "this item is temporarily unavailable try again later " I dont know what to do.

To install your original version of OS X:

Install Lion Through Yosemiteon a New HDD/SDD

Be sure you backup your files.

1. Restart the computer and after the chime press and hold down the Command-Option-R keys until a globe appears. Wait patiently - 5-15 minutes - until the Utility Menu appears.
2. Select Disk Utility from the Utility Menu and click on the Continue button.
3. After Disk Utility loads select the drive (usually, this is the out-dented entry with the mfgr.'s ID and size) from the side list. Click on the Erase tab in Disk Utility’s main window. A drop-down panel will appear.
4. Set the partition scheme to GUID then click. Set the Format type to Mac OS Extended (Journaled.) Click on the OK button and wait for the process to finish. Quit Disk Utility and return to the Utility Menu.
5. Select Install OS X from the Utility Menu and click on the Continue button.

If your computer can run Mountain Lion then it can run El Capitan or Sierra. These are what is available to you, now.

Upgrading to El Capitan

You can upgrade to El Capitan from Lion or directly from Snow Leopard. El Capitan can be downloaded from the Mac App Store for FREE.

To upgrade to El Capitan you must have Snow Leopard 10.6.8 or Lion installed. Download El Capitan from the App Store. Sign in using your Apple ID. El Capitan is free. The file is quite large, over 5 GBs, so allow some time to download. It would be preferable to use Ethernet because it is nearly four times faster than wireless.

Macs that can be upgraded to OS X El Capitan

1. iMac (Mid 2007 or newer) - Model Identifier 7,1 or later

2. MacBook (Late 2008 Aluminum, or Early 2009 or newer) - Model Identifier 5,1 or later

3. MacBook Pro (Mid/Late 2007 or newer) - Model Identifier 3,1 or later

4. MacBook Air (Late 2008 or newer) - Model Identifier 2,1 or later

5. Mac mini (Early 2009 or newer) - Model Identifier 3,1 or later

6. Mac Pro (Early 2008 or newer) - Model Identifier 3,1 or later

7. Xserve (Early 2009) - Model Identifier 3,1 or later

To find the model identifier open System Profiler in the Utilities' folder. It's displayed in the panel on the right.

Are my applications compatible? See App Compatibility Table - RoaringApps.

How to get macOS Sierra - Apple Support

The official list of Macs compatible with macOS Sierra:

2010 or Later

MacBook Air

MacBook Pro

Mac mini

Mac Pro

Late 2009 or Later

MacBook

iMac

Also, see The MacOS Sierra Compatibility List

How did you "reset" it?

If you want to install the original OS, you need to use internet recovery (Command + Option + R) at startup; once connected to Apple's servers, use Disk Utility to erase your drive. When finished, reinstall your original OS.

Did you boot up to internet recovery before using Disk Utility?