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When I turn on my Dell Optiplex 620, it automaticaly goes to the BIOS and says, click on safe mode, or safe network or best last start up or normal mode.

But when I click on normal it comes back to the same window. Then I click on safe mode and it works for about 5 minutes. Then it reboots itself every time.

What can I do? I checked to see if there was a virus and it's clean!!

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My Dell Optiplex 620 is not working properly. When I turn it on it goes automatically to BIOS and says click on safe mode or safe network or best last start up or normal mode.

Uhm no. That is not the BIOS. When you see that you are past the part where the BIOS performs POST and it has already started part of windows.

It means windows has detected that something went wrong when you last ran windows. If now pauses to offer you a few different start up options, so you can hopefully fix what is wrong.

but when I click on normal it comes back to that window. When I click on safe mode and it works for about 5 min then it reboots its self.

What can I do ?

You can try to find out what is wrong. There are a lot of things which can be wrong, but for starters check:

  1. CPU temperature. If it is overheating the computer will shut off hard. (if it is too hot, check if the fan is working)
  2. Some software problem in windows (check the event logs)
  3. A virus or worm. You write I checked if there was a virus and its clean, but you can not guarantee that if you check on a potentially infected computer. See this link.
  4. Sometimes windows will crash when the filesystem is corrupt. Pull the disk from the optiplex, put it in a different computer and do a disk check. (The point is to do the disk check without booting from the potentially broken windows disk).

Oh, and please use some capitalisation. And single exclamation marks are more than enough. A spell check would not hurt either.

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After doing what Hennes suggested, if that does not solve the problem or if bad (unrecoverable) sectors were found, buy a copy of Spinrite and run that on the drive. It often works wonders when there are damaged sectors that the OS chokes on (Note that those are rrrors below the file system, that e.g. checkdsk won't find/fix).

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As much as I love SpinRite this really should have been a comment. – Ramhound Sep 12 '12 at 14:01

When in safe mode:

sfc /scannow - this will fix system files if possible.

Boot related files are OK as you can boot.

sfc (system file check) could be run several times if errors are reported. You should have at least a stable Windows in safe mode to be able to do further fixings if necessary.

If booting normally to Windows still fails you have to disable all non-Windows startup items and enable one by one (with rebooting after every enabled item to see which item (program) is causing the problem.

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