I am using an HTC Wildfire S with Android 2.3.5. Recently my Android Market got automatically updated to the Google Play Store. I had to factory data reset due to some problem, Now I can see Android Market in phone and Android Market isn't updating to Google Play thus I am unable to access Google Play. I have already logged into Google Account in my device.
This happened to me previously. All I did was just wait and it eventually updated to Play Store.
I'd just say make sure you have a WiFi connection going on and have the Google Market app open. I think it will update itself after some time. I think it can just take a little while.
Have you tried opening Android Market from the home screen, with a data connection? I had a similar problem with Android Market details pages and web site and in-app payment methods being broken. Eventually I entered through the front door on the device and it made me OK all the new rules and started working again. Someone at Google screwed up and broke the app unless you use the home screen regularly, lol.