Error select r at the first screen to start repair

Assuming it is windows XP here are the steps to fix that error:
To complete part one, follow these steps:

1. Insert the Windows XP startup disk into the floppy disk drive, or insert the Windows XP CD-ROM into the CD-ROM drive, and then restart the computer.
   Click to select any options that are required to start the computer from the CD-ROM drive if you are prompted to do so.
2. When the "Welcome to Setup" screen appears, press R to start the Recovery Console.
3. If you have a dual-boot or multiple-boot computer, select the installation that you want to access from the Recovery Console.
4. When you are prompted to do so, type the Administrator password. If the administrator password is blank, just press ENTER.
5. At the Recovery Console command prompt, type the following lines, pressing ENTER after you type each line:md tmp
   copy c:\windows\system32\config\system c:\windows\tmp\system.bak
   copy c:\windows\system32\config\software c:\windows\tmp\software.bak
   copy c:\windows\system32\config\sam c:\windows\tmp\sam.bak
   copy c:\windows\system32\config\security c:\windows\tmp\security.bak
   copy c:\windows\system32\config\default c:\windows\tmp\default.bak
   
   delete c:\windows\system32\config\system
   delete c:\windows\system32\config\software
   delete c:\windows\system32\config\sam
   delete c:\windows\system32\config\security
   delete c:\windows\system32\config\default
   
   copy c:\windows\repair\system c:\windows\system32\config\system
   copy c:\windows\repair\software c:\windows\system32\config\software
   copy c:\windows\repair\sam c:\windows\system32\config\sam
   copy c:\windows\repair\security c:\windows\system32\config\security
   copy c:\windows\repair\default c:\windows\system32\config\default
   
6. Type exit to quit Recovery Console. Your computer will restart.

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To repair missing or corrupted system file/s, boot up with the Windows installation CD then - Press R to repair when instructed. Press 1 or Enter to repair the C:\Windows folder. Then type chkdsk /r and then press Enter. The repair process will take quite a long time.

1. Insert the Windows XP startup disk into the floppy disk drive, or insert the Windows XP CD-ROM into the CD-ROM drive, and then restart the computer.
   Click to select any options that are required to start the computer from the CD-ROM drive if you are prompted to do so.
2. When the "Welcome to Setup" screen appears, press R to start the Recovery Console.
3. If you have a dual-boot or multiple-boot computer, select the installation that you want to access from the Recovery Console.
4. When you are prompted to do so, type the Administrator password. If the administrator password is blank, just press ENTER.
5. At the Recovery Console command prompt, type the following lines, pressing ENTER after you type each line: md tmp
   copy c:\windows\system32\config\system c:\windows\tmp\system.bak
   copy c:\windows\system32\config\software c:\windows\tmp\software.bak
   copy c:\windows\system32\config\sam c:\windows\tmp\sam.bak
   copy c:\windows\system32\config\security c:\windows\tmp\security.bak
   copy c:\windows\system32\config\default c:\windows\tmp\default.bak
   
   delete c:\windows\system32\config\system
   delete c:\windows\system32\config\software
   delete c:\windows\system32\config\sam
   delete c:\windows\system32\config\security
   delete c:\windows\system32\config\default
   
   copy c:\windows\repair\system c:\windows\system32\config\system
   copy c:\windows\repair\software c:\windows\system32\config\software
   copy c:\windows\repair\sam c:\windows\system32\config\sam
   copy c:\windows\repair\security c:\windows\system32\config\security
   copy c:\windows\repair\default c:\windows\system32\config\default
   
6. Type exit to quit Recovery Console. Your computer will restart.

Note This procedure assumes that Windows XP is installed to the C:\Windows folder. Make sure to change C:\Windows to the appropriate windows_folder if it is a different location.

If you need more help come back.Post / thumbs / testimonial are welcome!

It is a registry problem.
Follow instructions from this link:

Windows could not start because the following file is missing or corrupt:
/WINDOWS/SYSTEM32/CONFIG/SYSTEM
You can attempt to repair this file by starting Windows Setup using the original Setup CD-ROM
Select “r” at the first screen to repair

So then i click r at the first screen and nothing happens...It keeps on repeating to repair on and on with the same message after i clicked r. I can't even access to the window...what can i do???

kindly follow these steps:

1. Insert the Windows XP startup disk into the floppy disk drive, or insert the Windows XP CD-ROM into the CD-ROM drive, and then restart the computer.
   Click to select any options that are required to start the computer from the CD-ROM drive if you are prompted to do so.
2. When the "Welcome to Setup" screen appears, press R to start the Recovery Console.
3. If you have a dual-boot or multiple-boot computer, select the installation that you want to access from the Recovery Console.
4. When you are prompted to do so, type the Administrator password. If the administrator password is blank, just press ENTER.
5. At the Recovery Console command prompt, type the following lines, pressing ENTER after you type each line: md tmp
   copy c:\windows\system32\config\system c:\windows\tmp\system.bak
   copy c:\windows\system32\config\software c:\windows\tmp\software.bak
   copy c:\windows\system32\config\sam c:\windows\tmp\sam.bak
   copy c:\windows\system32\config\security c:\windows\tmp\security.bak
   copy c:\windows\system32\config\default c:\windows\tmp\default.bak
   
   delete c:\windows\system32\config\system
   delete c:\windows\system32\config\software
   delete c:\windows\system32\config\sam
   delete c:\windows\system32\config\security
   delete c:\windows\system32\config\default
   
   copy c:\windows\repair\system c:\windows\system32\config\system
   copy c:\windows\repair\software c:\windows\system32\config\software
   copy c:\windows\repair\sam c:\windows\system32\config\sam
   copy c:\windows\repair\security c:\windows\system32\config\security
   copy c:\windows\repair\default c:\windows\system32\config\default
   
6. Type exit to quit Recovery Console. Your computer will restart.

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Thanks.
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it is nothing but windows registry error. do one thing in another pc download the Hiren's boot cd from internet, write that file in a cd, try to boot from that cd & repair the registry. otherwise just format the operating system & reload the OS.

boot your laptop from a xp cd and select repair option

this problem occurs when you try to update drivers in the computer..sometimes windows XP cannot update the driver and that corrupts system.ini file as it has a lot of bad entries..Due to this you will get this error mesage..No its not due to virus.its due to an attempt to change system.ini file

Windows could not start because the following file is missing or corrupt: \WINDOWS\SYSTEM32\CONFIG\SYSTEM

That means the System Registry Hive has become corrupted.

There are two ways to get back up and running. The easy way which doesn't always work, and then there is the hard way.

Easy Way --- Note that this doesn't always work.
When you are booting your system, press the F8 key during the start of the bootup sequence, meaning after it does the Power On Self Test.

Once you press the F8 key, you will be taken to a Menu. Select "Boot Using Last Known Good Configuration".

It will now attempt to load Windows XP using a past set of configuration files.

If that doesn't work, there is the next step....the hard way.

Hard Way
Boot your system with the Windows XP Install CD, let the system boot into the Setup. Once in the Setup, choose to run the Recovery Console.

You will now be presented with a screen similar to good old DOS.

First, we will recover the System Hive.

Now, type in the following commands with pressing Enter after each line.

md tmp
copy C:\windows\system32\config\system C:\windows\tmp\system.bak
delete C:\windows\system32\config\system
copy C:\windows\repair\system C:\windows\system32\config\system

Be very careful when you are typing in these commands, one wrong move, and you have, broken Windows XP.

Also, change the C in the commands to whatever your Windows XP drive letter is.

Attempt to boot the system, if it doesn't boot, get back into the Recovery Console and do the following commands.

md tmp
copy C:\windows\system32\config\software C:\windows\tmp\software.bak
delete C:\windows\system32\config\software
copy C:\windows\repair\software C:\windows\system32\config\software