doors on seat alhambra tdi 1999 will only lock from inside ?

doors on seat alhambra tdi 1999 will only lock from inside, drivers door locks manually using key. Tailgate locked won't open even with key. Had it checked no wires broken suggested replacing ecu behind dashboard...not under seat as with others...Has anyone every replaced one in the dash area....is it a big job...I normally do my own car maintenance?
Would appreciate some assistance.

Thanks