Suddenly my Sony can't find my operating system and will not boot up

Well if this is the case what you need to do is a Factory restore.
Do you have Sony Viao recovery media installed?

You can make recovery disks to restore your sons laptop back to factory reset.

If there here are no System Recovery CDs (SRCDs) included with the computer. The recovery data required to return the computer to the original, factory-installed condition is included on a special partition of the hard drive. Follow this procedure to create the Recovery Media Kit (a set of Recovery Discs), which can be used to restore the recovery partition and return the computer to the original, factory-installed condition.

IMPORTANT:

Rewritable media can be used to create the Recovery Discs, but are not recommended.
Not all computers have the capability to write to DVD media. Consult the specifications for the computer for additional information.
Do not interrupt the power during the recovery process.
NOTE: The Recovery Media Kit is not a backup utility. Personal data and software installed after purchase, or since the last system recovery, is not saved by the Recovery Media Kit.

Ensure all open programs are closed.
Ensure all network connections are disconnected.
Ensure all peripheral devices are disconnected.
NOTE: If the computer uses an external CD/DVD drive, ensure the drive is plugged in according to the instructions in the VAIO User Guide.

From within the VAIO Recovery Wizard application, in the Create Recovery Discs window, click Next .
NOTE: The Create Recovery Discs window can be reached through the VAIO Recovery Wizard main menu or by selecting the Create Recovery Discs option on the Start Menu.

Under Create Recovery Discs (Step 1 of 3) , click to select the option to use either DVD or CD media.
NOTE: The type of media that can be used and the number of discs required may vary depending on the type of disc drives present and the specific model used. Details are provided in the VAIO Recovery window.

Click the Next button.
At the Insert a blank... dialog box, insert the appropriate disc.
NOTE: The appropriate drive will open to receive the disc.

Click the OK button.
NOTE: If a This disc is not empty dialog box is displayed, click the OK button.

Insert a new disc when necessary as instructed.
When all the disks have been created, click the Finish button.
NOTE: After the Recovery Media Kit has been created the first time, any disc can be created again by selecting the disc from the list and clicking Next .

Or:


How to create the Recovery Media Kit using DVD discs.


Follow this procedure to create the Recovery Media Kit using DVD discs.

IMPORTANT:

Rewritable media can be used to create the Recovery Discs, but are not recommended.
Do not interrupt the power during the recovery process.

NOTE: The Recovery Media Kit is not a backup utility. Personal data and software installed after purchase, or since the last system recovery, is not saved by the Recovery Media Kit.

Ensure all open programs are closed.
Ensure all network connections are disconnected.
With the exception of the Digital Living System Media Changer, ensure all other peripheral devices are disconnected.
Connect the Media Changer to the computer.
Turn on the Media Changer.
Remove all discs currently loaded in the Media Changer.
Load two blank recordable or rewritable DVDs into the Media Changer.
On the taskbar , click the Start button, then click Media Center .
In the Media Center window, click More Programs .
In the MORE PROGRAMS window, click Manage Disks .
In the NEW DISCS FOUND dialog box, click the Yes button.
In the DISC SCAN COMPLETE dialog box, click the OK button.
Close the Media Center window.
NOTE: If the top of the Media Center window is not clearly visible, making it difficult to use the Close button, press ALT + F4 .

From within the VAIO Recovery Wizard application, in the Create Recovery Discs window, click Next .
NOTE: The Create Recovery Discs window can be reached through the VAIO Recovery Wizard main menu or by selecting the Create Recovery Discs option on the Start Menu.

Under Create Recovery Discs (Step 1 of 3) , click to select the Create recovery disc(s) using 2 recordable DVD(s) option.
Click the Next button.
In the Insert a blank DVD... dialog box, click the OK button.
NOTE: If an error occurs during the writing process, try another disc .

In the The disc was successfully created dialog box, click the OK button.
On the taskbar , click the Start button, then click Media Center .
In the Media Center window, click More Programs .
In the MORE PROGRAMS window, click Manage Disks .
In the MANAGE DISCS window, click the EJECT button next to the highlighted disc.
Remove the ejected disc and label it Recovery DVD 1/2 .
In the CONFIRM EJECT dialog box, click the Yes button.
Close the Media Center window.
NOTE: If the top of the Media Center window is not clearly visible, making it difficult to use the Close button, press ALT + F4 .

In the Insert a blank DVD... dialog box, click the OK button.
NOTE: If an error occurs during the writing process, try another disc .

Under Create Recovery Discs (Step 3 of 3) , click the Finish button.
NOTE: After the Recovery Media Kit has been created the first time, any disc can be created again by selecting the disc from the list and clicking Next .

On the taskbar , click the Start button, then click Media Center .
In the Media Center window, click More Programs .
In the MORE PROGRAMS window, click Manage Disks .
In the MANAGE DISCS window, click the EJECT button next to the highlighted disc.
Remove the ejected disc and label it Recovery DVD 2/2 .
In the CONFIRM EJECT dialog box, click the Yes button.
Close the Media Center window.
Also see below posts, it will help.

http://www.techsupportforum.com/security-center/general-computer-security/405860-factory-restore-sony-vaio-desktop.html

Hi,

May i know the Operating system running on the computer? What is the error message that you get?

Try if you are able to login to safe mode via Windows advanced boot options by hitting F8 while booting.

Please update me as soon you can.

Regards
Riztech