Intentionally deleted Android system - how do I fix this?

Right now I own a Sony Ericsson Xperia x10 mini and I rooted it. I had this program installed from Android Marketplace that allows you to delete applications. So guess what... I deleted several applications for testing purposes and I knew that if I uninstall Android System it would break everything. I did that epic "mistake" for testing purposes (don't try this). The thing is how do I fix this? I have spent some time reading through forums and installed Flashtool and downloaded the ftf file (X10a_v2.1.update-1_2.1.A.0.435_Generic.ftf) in C:\Flashtool\firmwares directory. What I have to deal with right now: - My mobile phone switched off when deleted Android System so I decided to boot it to see if any error messages comes up. - Now my phone won't power off due to the lack of Android System. So I have to use a torx screwdriver to remove the screws and take off the battery (because Flashtool requires the phone to be switched off) but unfortunately the Torx I have is one size bigger than the required one for Xperia's screws. - I guess I have to wait until the battery is dead or I should just get a proper Torx screwdriver. The thing is that I have another Xperia x10 mini as well (works for now - didn't try any uninstall) and connected it to FlashTool and followed the instructions to flash it but I keep getting this error message: >ERROR - ERR_SEVERITY="MAJOR";ERR_CLASS="SECURITY_CLASS";ER R_DYNAMIC="SIN header verification failed" I tried to figure out what's causing this and I end up with the "locked bootloader solution". I tried the instructions read here: http://unlockbootloader.sonymobile.com/instructions but when I typed ##7378423## no service menu was available... That happened to the working Xperia phone. How would I possible do that on a broken Xperia? Any suggestions would be highly appreciated! We're all learning through our mistakes after all.