I got alerted that I had the flashback virus and was told to download SOPHOS ant-virus software. I did this and did a scan once the scan had found the vrius I cleared it and ended the scan. I then turned off my MacBook and it won't turn back on again. It comes up with the apple symbol and that start up noise but it does not progress from there. The apple symbol turns into and error symbol and then dissapers. My computer then stays a grey colour. Any suggestions?!
It is very unlikely it is anything Flashback did directly that is affecting your booting. Installing virus scanning software is a lot more likely to be the cause of the problem.
Will your computer start in Safe Mode?
Mac OS X: Starting up in Safe Mode - http://support.apple.com/kb/HT1455
What is Safe Boot, Safe Mode? (Mac OS X) - http://support.apple.com/kb/HT1564
Safe Boot takes longer than normal startup - http://support.apple.com/kb/TS1884