deepthoughts

Hi i am new and am having a very perplexing problem happening and i am hoping maybe that someone might have solution,what is happening is that when i go to select Avast Antivirus>Stop Memory Scan>and then select Schedule Bootscan what happens is that it goes to restart and then i get a blue screen or dos i think and then it is just about to do a virus scan when an unexplain or something message pops up just for a split second not giving my computer tech or me enough time to really see the message and then it goes right back to Windows and my desk top without or bypassing the bootscan,now my computer tech is very good at solving these problems but this one has him perplexed!!!!Now i would greatly appreciate any input from you all as to what it could be as i would like to be able to do these bootscans also my tech made sure that Avast had the latest updates and did everything that he could think of so far. Thanks, Deepthoughts