Compounds which are 3,4-dihydro-2H-pyrazino[1,2-a]indol-1-one derivatives or pharmaceutically acceptable salts thereof, their preparation process and pharmaceutical compositions comprising them are disclosed; these compounds are useful in the treatment of diseases caused by and/or associated with an altered protein kinase activity such as cancer, viral infection, prevention of AIDS development in HIV-infected individuals, cell proliferative disorders, autoimmune and neurodegenerative disorders; also disclosed is a process under Solid Phase Synthesis conditions for preparing the compounds of the invention and chemical libraries comprising a plurality of them.