Cranks but wont start?

I bought a 1996 Nissan Sentra 6 months ago with 234,000 miles on it. It started lurching a little intermittently while driving. Then two months ago it wouldn't start. The shop replaced spark plugs and cleaned fuel out of 1 cylinder (assumed at the time that flooding was from repeated attempts to start by AAA guy). Plug tips look white, so my roommate (who's a gearhead) told me that the fuel:air ratio is not right, running lean. So he showed me how to clean tips and check gap, which I have been doing about every other week until last week. Now won't start again. Same thing as last time, cranks but does not turn over. Roommate removed one plug and told me it's not getting any spark. What's up? Is this a common problem with this car?