i have seen systems become pretty unstable when both were installed yes, but never have i seen it completely corrupt your laod to the point that safe mode will not even work. if you were unable to access safe mode before you messed with your recovery disks and such, then i would guess that yes, a virus probably had some part in it.

i have seen many people install multiple av programs as well as trojan hunters, etc, thinking this will double their protection. usually, all that happens is that the programs end up conflicting with each other, disabling each other, etc, nullifying the original purpose of installing them in the first place. you friend may be a good example of this; installing two systems, yet still getting hit with a possible virus.

i always say choose which ever one is your favorite and has the most friendly interface for you. make sure you are always up to date and run scans regularly.