Q:
A: Yes, in fact it can completely crash your system because one AV program will view the operation of the other as virus activity. The reason is av softwares alter your boot record which is what most viruses do. So remove one of them. It's normal to run several different malware/spyware/grayware removal softwares but not at the same time. Typically it's best to run a single av solution, and have several spyware/malware scanners on hand.