There are basically four ways to restore our phone to usability, and usage somewhat depends upon how heavily is your system damaged
If our phone does not load the system (so we're stuck at SE logo on boot) and we have xRecovery, we can flash the last working backup. This is as clear as it can be, provided that you need to know something already to install xRecovery.
For those who don't know what it is: it's a boothack, which allows to backup and restore all the data stored on phone memory, install custom zips and do other cunning stuff
http://forum.xda-developers.com/showthread.php?t=878426 - here's how to install it, enjoy.
Flashtool is a software developed for Xperia X10, with later added functionality for our precious X8.
It comes in handy when two things happen: we cannot, for whatever reason, enter xRecovery and we don't want to/cannot use SEUS or PCC.
How to use?
1. Download latest version from this thread: http://forum.xda-developers.com/showthread.php?t=920746
2. Download ROM image, whichever you prefer:
X8 Shakira E15i_2.1.1.A.0.6_generic.ftf
3. Download the baseband if you want to flash it (custom ROMs like miniCM or CM7 require baseband ending with "15" in order for app2sd to work):
4. Place ftf file in /firmwares directory of your flashtool.
5. Install drivers from /drivers directory (if your antivirus doesn't like them, disable the antivirus :P)
6. Prepare yourself - plug the USB cable to the computer (NOT TO THE DEVICE YET) and launch flasher.
7. Click "flash", choose your ROM from the list, wait for instructions.
8. When the instruction pops up, press and hold "back" button on your X8 and plug the cable into it. Keep holding untill you see that flashing of files has begun, then you may release it.
9. Flashing will take a while, you may observe the progress on a bottom bar. When it's finished you will be asked to plug off your device and reboot it.
10. Tadam! It's functional again! Clean installation which you may screw up again
11. If you wish to change baseband, clean firmware directory in flashtool and place baseband ftf file in it, then go through flashing procedure again.
3. SEUS/PCC flashing
Most probably the most prototipical way to deal with it. PCC is PC Companion, soft that you obtain on your SD card along with your device, or you can download from SE website: http://www.sonyericsson.com/cws/supp...10?cc=gb&lc=en
Once downloaded and installed, launch it. Most probably it will download some updates. Then choose device updating and follow the instructions. As for flashing - the procedure with holidng back button is the same as with flashtool.
As PCC is heavy and buggy, we are presented with an alternative - SEUS, the Sony Ericsson Update Service. You may download it here: http://www.sonyericsson.com/cws/supp...10?cc=gb&lc=en
Once installed and launched, SEUS will start looking for updates. Let it take its time. After a while you will be presented with a board full of phones. Choose your Xperia from the list and continue. You will be asked to flash your phone, analogically as in flashtool in point 2. After flashing is done, SEUS will download the latest SE ROM available for your device and flash it.
Flashtool, PCC and SEUS will cause loss of data such as contacts, stored messages, installed apps and so on. Anything that exists in phone memory will be erased.
Flashing a backup in xRecovery will cause similar data loss. However, it is possible to flash only system or only data backup in xRecovery. Some ROMs (like miniCM) are updated by update.zip which erases only /system folder, leaving personal data and installed apps intact.
However, you need to be able to enter xRecovery mode in order to use it, SEUS and flashtool do not require enabling the phone. PCC requires the phone to be turned on first in order to recognize it correctly, so it's more update-oriented.
Hope someone will benefit. If you see any mistakes, in spelling, grammar or content, let me know and I will correct it!