Why does Mountain Lion triggers front fan in Mac Pro?

Try resetting the SMC http://support.apple.com/kb/ht3964

Faulty installation. Why could you not install the SSD in the Mac Pro running Leopard? Why are you running Leopard in the Mac Pro instead of upgrading it to Mountain Lion? Try doing it this way. Put the SSD into the Mac Pro.

Erase and Install

1. Boot from your OS X Installer Disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu.

2. After DU loads select your SSD (this is the entry with the mfgr.'s ID and size) from the left side list. Note the SMART status of the drive in DU's status area. If it does not say "Verified" then the drive is failing or has failed and will need replacing. SMART info will not be reported on external drives. Otherwise, click on the Partition tab in the DU main window.

3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed.

4. After formatting finishes quit DU and return to the installer. Install Leopard onto the SSD.

Upgrade Paths to Snow Leopard, Lion, and/or Mountain Lion

You can upgrade to Mountain Lion from Lion or directly from Snow Leopard. Mountain Lion can be downloaded from the Mac App Store for $19.99. To access the App Store you must have Snow Leopard 10.6.6 or later installed.

Upgrading to Snow Leopard

You must purchase Snow Leopard through the Apple Store: Mac OS X 10.6 Snow Leopard - Apple Store (U.S.). The price is $19.99 plus tax. You will be sent physical media by mail after placing your order.

After you install Snow Leopard you will have to download and install the Mac OS X 10.6.8 Update Combo v1.1 to update Snow Leopard to 10.6.8 and give you access to the App Store. Access to the App Store enables you to download Mountain Lion if your computer meets the requirements.

Snow Leopard General Requirements

1. Mac computer with an Intel processor

2. 1GB of memory

3. 5GB of available disk space

4. DVD drive for installation

5. Some features require a compatible Internet service provider;

fees may apply.

6. Some features require Apple’s iCloud services; fees and

terms apply.

Upgrading to Lion

If your computer does not meet the requirements to install Mountain Lion, it may still meet the requirements to install Lion.

You can purchase Lion by contacting Customer Service: Contacting Apple for support and service - this includes international calling numbers. The cost is $19.99 (as it was before) plus tax. It's a download. You will get an email containing a redemption code that you then use at the Mac App Store to download Lion. Save a copy of that installer to your Downloads folder because the installer deletes itself at the end of the installation.

Lion System Requirements

1. Mac computer with an Intel Core 2 Duo, Core i3, Core i5, Core i7,

or Xeon processor

2. 2GB of memory

3. OS X v10.6.6 or later (v10.6.8 recommended)

4. 7GB of available space

5. Some features require an Apple ID; terms apply.

Upgrading to Mountain Lion

To upgrade to Mountain Lion you must have Snow Leopard 10.6.8 or Lion installed. Purchase and download Mountain Lion from the App Store. Sign in using your Apple ID. Mountain Lion is $19.99 plus tax. The file is quite large, over 4 GBs, so allow some time to download. It would be preferable to use Ethernet because it is nearly four times faster than wireless.

OS X Mountain Lion - System Requirements

Macs that can be upgraded to OS X Mountain Lion

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.

For a complete How-To introduction from Apple see Upgrade to OS X Mountain Lion.

The installed systems will not be the same. There is missing or incorrectly configured software installed that works on the MBP but not on the MP. Why not try connecting the two via Firewire cable. Boot the Mac Pro into Target Disk Mode then boot the MBP using the Snow Leopard DVD. Install Snow Leopard onto the MP. Be sure you use a retail Snow Leopard disc. Don't use any discs that came with the MBP.