Cubase LE 5 - WAV file imported into a channel won't play

Before going through a re-installation you might try “trashing your prefs”.

https://www.steinberg.net/en/support/knowledgebase_new/show_details/kb_show/removing-the-preferences-of-the-sequencer/kb_back/2025.html?tx_p77sbknowledgebase_pi1[keyword_search]=Preferences

You just might get lucky.