How can i master reset my sony vaio vgn ux280p

You can contact Sony tech support:
http://esupport.sony.com/US/perl/select-system.pl?DIRECTOR=CONTACT

or Skype with this seller:
http://www.ebay.com/itm/Sony-VAIO-Onetime-Password-Unlock-locked-BIOS-asking-4-ONETIME-Password-VGN-VPC-/300718473553?pt=LH_DefaultDomain_0&hash=item460437c151

If you have enough room on your drives, copy the Windows disc complete to the hard drive and run setup from the hard drive.

You need to contact the seller. If the laptop was not stolen, the seller will give you that information. If not, return it to the seller for a refund. There are a lot of stolen items auctioned through ebay and others. Legitimate sellers will help you.

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Give this a try:
When the VAIO logo appears on the computer's screen, briefly press the F10 key on the computer keyboard.

The VAIO Recovery Wizard appears.

Hope this helps.

Sony Vaio newer models generate a 16 digit error when you enter 3 wrong passwords "xxxx-xxxx-xxxx-xxxx" , i just unlocked my Sony Vaio VGN-CZ model with this code in laptoprebirth.com

http://www.docs.sony.com/release/VGNUX280P.pdf

On page 146 of the manual it says you have to take it to a service center, this tells me the device needs to be opened to trip the bios battery. If BIOS reset is not part of your warranty then you will need to either pay a service center or open the device yourself remove the BIOS battery, turn the computer on then off and replace the BIOS battery. The BIOS will be reset to default and your BIOS password cleared. REMEMBER opening the device WILL VOID WARRENTY!!!

In that case, you may perform C: Drive Restore using the Recovery Partition. You may access the Recovery Partition by restarting the Computer and tapping the F10 key for 10 to 15 seconds. Please select the "Restore C: Drive" in the VAIO Recovery Center.

Usually a bad screen or video inverter.Sometimes the video card is bad even with a white screen instead of a black one.

Sony eSupport - VGN-UX280P - Manuals / Specs / Warranty
http://esupport.sony.com/US/perl/model-documents.pl?mdl=VGNUX280P