Valves, as used in an old wireless/radio, is not used in modern computers.
they were huge and you needed loads
Reliability and heat were the main problems. Valves were fragile devices that, due to the relatively primitive way they were manufactured, failed pretty quickly. In addition to that, they gave off vast amounts of heat. This meant they needed expensive air-conditioning systems to keep their temperature down.
using valves
Mechanical valves are effective but can increase the incidence of blood clots.
Probably rate of burnout and heat. But this was common to all vacuum tube computers, not just Colossus.
Valves
To many people dying and changing valves for something else
To many people dying and changing valves for something else
discrete transistors
what are some problems conected with computer investigations
There are no valves in a modern computer. If by valves you mean vacuum tubes, the equivalent is a transistor. Modern CPUs have many transistors/gates on their dies. The SandyBridge i7, a near-top end general purpose computer COU can have 2.2 billon transistor elements on the CPU die. Of course there are many more transistors incorporated in the logic chips, controllers and video cards in a computer as well.
The Colossus computer worked using one to two thousand thermionic valves.