You could but then you lose performance of your SSD. Best performance comes from a fresh install.
Obviously the boot files from your previous OS didn't get deleted. I can't remember if 7 is the same as XP but try going into the msconfig utility, click on the boot.ini tab, click on check all boot paths and it should detect a bad entry.
To get into the msconfig utility click on start, and in the search box type msconfig hit enter.