THE BRONX - Flames ignited inside the basement of a building on 138th Street this morning, filling a Mexican restaurant on the first floor with smoke.Firefighters who responded to the call say it appears that the fire was caused by an electrical problem. Fire Chief Jim Donlevy says once the flames were extinguished, firefighters proceeded to abate the high levels of carbon monoxide that were detected on the upper floors of the building. No one was injured. The fire did not affect the restaurant above the basement, but it sustained some water and smoke damage. The owner hopes to clean up the eatery and reopen by Monday.