I have recently purchased two sites off of flippa. One was ranked page 4 or 5 for the main keywords and the other was number 3 on page one. They were down for about 15 mins while they transfered them to my hosting. The first site is nowhere to be found in the serps now and the one that was 3rd is now page 5. I started building links immediately through article submissions. Any thoughts on the dramatic drops? Could it be due to the downtime? My only other guess is Google doesn't care for my link building with these sites. I thought maybe the previous owners deleted some links that were pointing to them but the first site didn't have any so I threw that theory out the window.
try to check the back links...maybe changing the hosting is not a good idea after... try to ask the previous owner what link building technique they do or you can find it in checking the back links.
google might crawled the site when its down.. just continue building some quality links on it so google can recognize it..