[Xperia Play Q&A, Help & Troubleshooting] DSoundso:
Hm, didn't work. Now it's getting really strange.

I still can't access the recovery mode, it just boots. I unlock the screen, enter my pin and after some seconds the phone just reboots.

Here the logfile from flashtool:

10/059/2013 12:59:30 - INFO - <- This level is successfully initialized

10/059/2013 12:59:31 - INFO - Flashtool Version 0.9.9.0 built on 2012-11-13 22:53:30

10/059/2013 12:59:31 - INFO - You can drag and drop ftf files here to start flashing them

10/059/2013 12:59:40 - INFO - Device disconnected

10/000/2013 13:00:00 - INFO - Device connected in flash mode

10/000/2013 13:00:11 - INFO - Selected R800i_4.0.2.A.0.62_phoenixvendor.ftf

10/000/2013 13:00:11 - INFO - Preparing files for flashing

10/000/2013 13:00:40 - INFO - Device disconnected

10/000/2013 13:00:43 - INFO - Please connect your device into flashmode.

10/001/2013 13:01:05 - INFO - Device connected with USB debugging off

10/001/2013 13:01:05 - INFO - For 2011 devices line, be sure you are not in MTP mode

10/001/2013 13:01:10 - INFO - Device disconnected

10/001/2013 13:01:39 - INFO - Device connected in flash mode

10/001/2013 13:01:40 - INFO - Opening device for R/W

10/001/2013 13:01:40 - INFO - Reading device information

10/001/2013 13:01:40 - INFO - Phone ready for flashmode operations.

10/001/2013 13:01:40 - INFO - Start Flashing

10/001/2013 13:01:40 - INFO - Processing loader

10/001/2013 13:01:40 - INFO - Checking header

10/001/2013 13:01:40 - INFO - Flashing data

10/001/2013 13:01:42 - INFO - Loader : S1_Loader_Root_773f - Version : R4A066 / Bootloader status : ROOTED

10/001/2013 13:01:43 - INFO - Processing kernel.sin

10/001/2013 13:01:43 - INFO - Checking header

10/001/2013 13:01:43 - INFO - Flashing data

10/001/2013 13:01:45 - INFO - Processing fota1.sin

10/001/2013 13:01:45 - INFO - Checking header

10/001/2013 13:01:45 - INFO - Flashing data

10/001/2013 13:01:46 - INFO - Processing fota0.sin

10/001/2013 13:01:46 - INFO - Checking header

10/001/2013 13:01:46 - INFO - Flashing data

10/001/2013 13:01:47 - INFO - Processing adsp.sin

10/001/2013 13:01:47 - INFO - Checking header

10/001/2013 13:01:47 - INFO - Flashing data

10/001/2013 13:01:49 - INFO - Processing amss.sin

10/001/2013 13:01:49 - INFO - Checking header

10/001/2013 13:01:49 - INFO - Flashing data

10/002/2013 13:02:00 - INFO - Processing amss_fs.sin

10/002/2013 13:02:00 - INFO - Checking header

10/002/2013 13:02:00 - INFO - Flashing data

10/002/2013 13:02:01 - INFO - Processing vendor.sin

10/002/2013 13:02:01 - INFO - Checking header

10/002/2013 13:02:01 - INFO - Flashing data

10/002/2013 13:02:38 - INFO - Processing system.sin

10/002/2013 13:02:38 - INFO - Checking header

10/002/2013 13:02:38 - INFO - Flashing data

10/004/2013 13:04:45 - INFO - Processing userdata.sin

10/004/2013 13:04:45 - INFO - Checking header

10/004/2013 13:04:45 - INFO - Flashing data

10/004/2013 13:04:47 - INFO - Processing cache.sin

10/004/2013 13:04:47 - INFO - Checking header

10/004/2013 13:04:47 - INFO - Flashing data

10/004/2013 13:04:48 - INFO - Ending flash session

10/004/2013 13:04:48 - INFO - Flashing finished.

10/004/2013 13:04:48 - INFO - Please unplug and start your phone

10/004/2013 13:04:48 - INFO - For flashtool, Unknown Sources and Debugging must be checked in phone settings

10/004/2013 13:04:48 - INFO - Device connected in flash mode

10/005/2013 13:05:10 - INFO - Device disconnected

10/005/2013 13:05:12 - INFO - Log written to C:\Programme\Flashtool\flashtool_2013-03-10_12-59-30.log

10/005/2013 13:05:24 - INFO - Device connected in fastboot mode

10/005/2013 13:05:28 - INFO - Launching Fastboot Toolbox 1.0 by DooMLoRD

10/005/2013 13:05:29 - INFO - Device Status: FASTBOOT mode

10/005/2013 13:05:37 - INFO - Selected kernel (boot.img or kernel.sin): E:\Programme\Handy\LuPuS-STOCK-GB+ICS-v1-720.img

10/005/2013 13:05:37 - INFO - Flashing selected kernel

10/005/2013 13:05:40 - INFO - sending 'boot' (7552 KB)...

10/005/2013 13:05:40 - INFO - (bootloader) USB download speed was 3866624kB/s

10/005/2013 13:05:40 - INFO - OKAY [ 0.833s]

10/005/2013 13:05:40 - INFO - writing 'boot'...

10/005/2013 13:05:40 - INFO - (bootloader) Download buffer format: boot IMG

10/005/2013 13:05:40 - INFO - (bootloader) Flash of partition 'boot' requested

10/005/2013 13:05:40 - INFO - (bootloader) S1 partID 0x00000003, block 0x00000280-0x000002e3

10/005/2013 13:05:40 - INFO - (bootloader) Erase operation complete, 0 bad blocks encountered

10/005/2013 13:05:40 - INFO - (bootloader) Flashing...

10/005/2013 13:05:40 - INFO - (bootloader) Flash operation complete

10/005/2013 13:05:40 - INFO - OKAY [ 1.477s]

10/005/2013 13:05:40 - INFO - finished. total time: 2.310s

10/005/2013 13:05:40 - INFO - FASTBOOT Output:

sending 'boot' (7552 KB)...

(bootloader) USB download speed was 3866624kB/s

OKAY [ 0.833s]

writing 'boot'...

(bootloader) Download buffer format: boot IMG

(bootloader) Flash of partition 'boot' requested

(bootloader) S1 partID 0x00000003, block 0x00000280-0x000002e3

(bootloader) Erase operation complete, 0 bad blocks encountered

(bootloader) Flashing...

(bootloader) Flash operation complete

OKAY [ 1.477s]

finished. total time: 2.310s

10/005/2013 13:05:40 - INFO - Please check the log before rebooting into system

10/005/2013 13:05:42 - INFO - Finished Fastboot Toolbox

EDIT

Hm, rooky mistake. I pressed backwards key instead of volume down. Oh my -_-

Thanks for your help!