Interesting, are you using firefox or chrome?
There may be a very obvious fix, if you just reinstalled your OS have you updated your browser versions?
Here's a possible solution if you are using firefox (I don't know too much about Chrome):
-> Select menu, then options.
-> select advanced.
-> Select general.
->uncheck "check my spelling as I type".
If that doesn't work, right click and select "Add dictionaries" and then add English.
If your problem is chrome related, get firefox & then uninstall chrome