Trojan - Boot Sequence

I have a problem with my PC. A few days ago I received a URL in MSN messenger that infected me with a trojan horse when I entered the site.

Since then, AVG antivirus has popped up every time I startup my computer and has told me "threat detected - trojan horse downloader." I proceed to heal the file, yet next time I start up the same thing happens. The file name is simply "installer.exe". Immediately after this, my internet explorer opens and opens "web.links4all.biz",which I believe re-infects me. Since then, I have worked with my PC for a few days, with the intention of coming on here and sorting out the problem when I get the chance, unfortunately, the problem has escalated.

During my usual practice, AVG popped up saying "threat detected" once again. This time, the problem was "Trojan horse flooder." I told it to heal the file, it said it was healed, but told me I had to restart my computer for the process to complete.I restarted my computer, but after the first windows loading screen, the system shuts off and automatically reboots, until it reaches this point where the same thing happens.

I've tried using safe mode, and nothing has changed, it still enters the cycle of restarting continually.