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Which version of Vista are you using (Home Basic or Home Premium), is it 32-bit or 64-bit, and is SP2 installed and is it fully up-to-date on updates? Is Outlook (or Office if you have a Suite) also fully up-to-date with updates?
How did Outlook close the last time you used it? Did you shut it down gently - normally? Did you hit shutdown or restart while it was still open? Did you lose power and the computer completely shut down hard? When was the last time you used it successfully and did you have any problems at all (even the slightest hint of a problem)?
Please give the EXACT error message you are getting (word-for-word including any codes). Does this occur as soon as you click the icon or do you see the Outlook Logo and then it appears or do you get to see the screen and then it appears? Are you using Outlook Connector? Go to Start / All Programs / Accessories / Command prompt and right click on command prompt and click run as Administrator. While in Command Prompt, type chkdsk /f /r and enter and let it run. It will want to schedule itself to run at the next restart. Answer yes and then reboot to run the program. It will scan and try to fix any corruption or bad sectors on your hard drive and mostly remove that as a potential cause. You say you tried the repair option from the disk. Did it give you any messages - if so, what EXACTLY (word-for-word)? If the above doesn't help, search the entire C: drive in Vista for scanpst.exe (the one that should be somewhere in some folder in the Program Files directory - there may be others but this is the one you want); Go to Start / Search Box and type in scanpst.exe. As you're typing you'll see two hyperlinks appear just above where you're typing and one will say Search Everywhere. Click on that. That will do a quick indexed search and bring up a dialog box. Click on Advanced Search. Click on the location drop down menu and find Drive C: and click on it. Check the box "include non-indexed, hidden, and system files (may be slow)." Then click on Search. You will now be searching your entire hard drive for the specified file. And yes, it's not a very efficient way of searching the entire drive for a file but that's how it's done in Vista. Once you find it, double click on it to run it and point it to your Outlook.pst file (the one you are using) and it will scan and hopefully repair the .PST file. When it's done, try opening Outlook and see if that helped. If that doesn't work, I'm afraid I'm out of free alternatives. There are a number of commercial software products that claim to be able to repair .PST files. Most seem to cost $49 - or at least you can find several at that price. I couldn't find any freeware. Some offer free trials so you can see if it will work by showing you what it can recover (but to save it and use it, you need to then puchase the product). I don't have any particular one to recommend as I've never used any of them. Here are links to some lists of options: Free Pst File Repair Freeware Downloads: MS Outlook Recovery by MS Outlook Recovery Tool, Repair PST Software by Disk Recovery Software and More or you can try pst repair vista freeware, shareware, software download - Best Free Vista Downloads. Make certain before you choose, it you decide to do this, that the product clearly states it is compatible with your version of Vista. I make no guarantees that any of these products will work or actually do the job - I recommend you choose one that offers a free trial or demo to show you it can actually restore your file - then it's much more likely to work when you buy it (the others you won't have a clue about until you've already purchased them and then they may or may not give you a refund even if it didn't work). If that doesn't work, I'm afraid that the file may be beyond repair or recovery. I hope you have a recent backup so that once it is restored at least all you'll lose is everthing since the backup. I hope this helps. Good luck!