How do I reset my Sony Xperia if I can't unlocked

yes

http://www.hard-reset.org/factory-default/how-to-easily-master-format-sony-xperia-m-c1904c1905-c2004c2005-dual-with-safety-hard-reset/
Hope this helps.
You installed anti virus?

To obtain an unlock code, you usually have to pay for a service. (not free) The top Google result:

http://cellphoneunlocker.com/

This is due to the corrupted GOOGLE APPS (market application)
Try master reset, if possible.
It could work.

If does not work, still there is a solution.

sony ericsson sim network pin

Free Unlock code is not possible to get for Sony Ericsson Xperia Play.It's latest Phone...You need to pay for it...Visit the site Simpleunlocking.com/sony-ericsson-xperia-play/rs16wp9/ get Unlock code and get Free Unlocking instructions at Mobileunlockguide.com/sony-ericsson-xperia-play and unlock it step by step.

To, Which network has your Sony Ericsson Xperia Neo V has been locked to? You can get the unlock code for a Sony Ericsson Xperia Neo V from www.unlocking4u.com/sony-ericsson-xperia-neo-v/rs6wp9/ at affordable cost. all the best mate.
Here are the steps for unlocking a Sony Ericsson Xperia Neo V:
1. Switch ON your Sony Ericsson Xperia Neo V with a Not Allowed SIM Card.
2. Your Sony Ericsson Xperia Neo V will request to enter an unlock code.
3. Tap the box where you have to input the code and a number pad will appear.
4. Type in the unlock code we send to you.
5. Press the 'Unlock' button on the phone.
6. Your Sony Ericsson Xperia Neo V phone should now be unlocked.

This method should work for you.
From the Home screen, drag upwardsSelect Settings > SD card, USB Mass Storage & phone storage > Factory data reset > Reset phoneEnter your screen unlock patternTap Erase everything.
Warning: Make sure you have backed up app important data you have on the phone before you reset the phone, because everything will be deleted.
Good Luck.
Thanks for using FixYa.

If you're looking to use the phone on other carriers aside from the original one, then you would need to unlock it first using the unique unlock code that's for your phone only.

Unlock Sony Ericsson Xperia X10