Good afternoon Scorp
.
First i have a question.... the damaged hard drive you removed... is that the disk where the OS (Windows i assume) was installed on? Or was it just a second hard drive only used to store data/install games or programs?
If it was a data storage disk:
When the monitor gets no signal, that usually means theres a plug loose. Unplug the computer from power supply (after shutting it down of course) and check ALL the plugs inside. Also make sure your graphics card is still solidly in the slot on the mother board. Then check all the plugs from the cables in the back. Especially the one going to the monitor.
If it was your system disk:
Also check all plugs.
What EXACTLY does the computer do when you try to start it up? How far do you get, ie at what point does the monitor not get any signal? Do you still see the "memory check" thingy and the point where it asks you to "hit DEL to enter setup"?