I have installed xp in my computer and it is updated automatically.
Sometimes when I open the system I get the following error message.
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Windows must restart now because the DCOM Server Process Launcher Service terminated unexpectedly.
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the system then restarts automatically.
It is not happening always, only sometimes.

What could be the reason?

a trojan /virus

I have been reading through some google search results and as soon as you get to the desktop quickly double click on the clock and roll back a few hrs ,this will give you a chance to run you antivirus program ,and may i suggest this scan also .
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Download Malwarebytes' Anti-Malware (http://www.majorgeeks.com/Malwarebytes_Anti-Malware_d5756.html) to your desktop.

* Double-click mbam-setup.exe and follow the prompts to install the program.
* At the end, be sure to checkmark the Update Malwarebytes' Anti-Malware and Launch Malwarebytes' Anti-Malware, then click Finish.
* If an update is found, it will download and install the latest version.
* Once the program has loaded, select Perform full scan, then click Scan.
* When the scan is complete, click OK, then Show Results to view the results.
* Be sure that everything is checked, and click Remove Selected.
* When completed, a log will open in Notepad.
post the log back here

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and download and run hijackthis don't fix anything with it just yet ,but save the log file and copy paste it here .
http://www.majorgeeks.com/downloadget.php?id=3155&file=15&evp=3304750663b552982a8baee6434cfc13

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