If it won't open at all then you may have to do a factory reset (remembering to back up all your important data first), but if it opens but won't load web pages:
Update Nokia Xpress Browser to the latest version:
Open your Nokia Xpress Browser from the menu.
In the address field, write download.browser.ovi.com.
From download.browser.ovi.com, download and install the latest version of Nokia Xpress Browser.
The new version automatically replaces your older one.
If all else fails, try downloading Opera Mini, which also compresses data here