Unable to use my OST file.

You may be able to "attach" the old OST to a new profile. I found these instructions that could get you what you need but I've never tried it personally:

Log into the new pc & create a new outlook profile (set it up as NOT in cached mode).

Copy the old ost file into the C:\Users\%userprofile%\AppData\Local\Microsoft\Outlook\ folder (assuming Windows 7)

In Outlook, go to the "File" ribbon, "Account Settings" button --> "Account Settings"

On the "E-Mail" tab, select your mail profile & click "Change" button.

Click the "More Settings" button, then click on the "Advanced" tab.

Click "Outlook Data File Settings" button, then the "Browse" button to select the ost file you just copied in.

Click "OK" a couple times to get back to the "Change Account" screen, and select the "Use Cached Exchange Mode" box.

Hit the "Next" button once or twice to finish the process, then restart outlook. Old ost file should be in use now.

http://community.spiceworks.com/topic/414188-attaching-old-ost-file-too-new-profile

thank you renazonse.. I tried this it said the file is not an pst file, even after changing the extension to PST.. any other solutions?

You can't use it as a PST since the database structure is different. You would have to follow the instructions exactly as stated above. If it doesn't work I know of no other way to utilize the OST other than a paid tool to extract the data.

Doesn't work.. Simply you can't do it..
I have tried it, you need more then just the OST file to get it to work..
Your only option is to do a manual archive at your office, and export your entire mailbox to PST file and use that..

You can use programs that claim they work, all you want, but there are parts of the OST file that require additional pieces of registry keys, etc to work correctly.. and if you don't have them.. save your time and money..

As noted, there are a variety of third party tools to convert an OST. The free ones do not always work. The ones that probably will work cost money.

Try the Stellar OST to PST converter. It is not free but it has been known to work.

http://osttopstconverter.stellarservertools.com/?gclid=CjwKEAiA4_WjBRCNgf7A_KeE9jwSJADtegYd8s0lAOEGkWPCat6D0kollMFXwmZgC6K8a_eXZlmEoxoC-trw_wcB

OST files aren't designed for what you're trying to do. They are used to chache data from the server for IMAP or Exchange accounts, and they can only be used on the computer that created them. If you just want to access the data (and not have real-time access in Outlook), you can use the free Kernel OST Viewer. But if you actually want to import that data into Outlook, you'll have to get the data extracted into a PST file first, and there are a bunch of utilities thtat do that (but none of htem are free). Here is a link to Kerel's conversion tool: http://www.nucleustechnologies.com/exchange-ost-recovery.html

I could not find the solution the way i wanted but managing with a OST viewer.. Thank you all.

I could not find the solution the way i wanted

What does this mean? You asked (your first post) how to convert to PST and at least a couple of the utilities we posted work and will convert an OST file.

Thank you