i let a trojan get in my pc to crack anno 2070. a couple days after i tried to boot my pc and it doesn't show, just reboots again and again. Can a trojan fry my pc and does anyone know the solution of this problem?
First off, Yes a virus can cripple your Bios, But this is rare.
To check, simply disconnect your HDD, stick your Windows installation disk in and see if the installation screen comes up. If it does, then wipe your forhead and do as rolli59 suggested - reinstall windows.
No you Can't FRY your motherboard nor can virus or trojan, (those things want to steal your data and newer bee noticed in most cases)
But looks like something messed with your windows (virus made to annoy people)
Good solution is to scan the hard drive outside the window (attach to external usb dock) to see what you dealing with (maybe name of virus) then apply the patch or fix
Also you can download boot CD like Ubuntu so you can use computer while fixing it. (internet, mail, etc) http://www.ubuntu.com/
^ You're correct in that you can not "fry" the MB; However there are a few malware programs (the really bad ones) that can mess up the BIOS. But they are not that common. Then there are the programs that mess up the boot sector of a HDD.
The First step is to determine what has been affected.
If you can boot to the bios and or boot to d DVD (ie the windows Instalation disk) then it is safe to conclude that the Bios is OK and the problem is on the HDD (Most Logical).
If this is correct then probably the best course of action would be to reinstall windows.
You could download the UBCD which has utilities on it to scan the HDD.
Hopefully you have BACKups of the files/data that you have created.