Where is the first computer now?

Scrapped.

Only modern recreations exist of the Atanasoff Berry Computer and Colossus. The MIT Differential Analyzer (mechanical analog) and Harvard Mark 1 (electromechanical) are completely gone. Roughly half a dozen of the 40 panels of ENIAC still exist and four of those work.

The modern recreations and the remaining ENIAC panels are in museums.