Help!! Computer wont turn on after upgrades.!!

Well, actually my computer does go on, but nothing happens after that.

My specs are an overclocked Q6600 at 3.1 Ghz, 2 gigs of ram ddr3, P35 mobo, and a 9800 GX2.

It was working perfectly fine.

Today I installed an additional HDD (1 TB) and 2 more gigs of ram. When I installed the RAM, due to wiring issues, I had to swith my current RAM to the other dual channel spot, but then I simply placed the new ram (same thing of course) in the other spots, so that should work. For the HDD, I put it in its slot, connected a new SATA power cable to the PSU, and I connected the other SATA cable to a SATA cable reciever on the mobo where other HDD are installed.

Now when I turn the computer on, it goes on like normal, the fans go, everything goes, but nothing appears on my screen, and my mouse and keyboard arent exactly connected (they normally light up, but they arent lit up).

So thats the story, any help is appretiated.

is it safe inserting wires inside a comp while its running?-PS360-

you just have to have fast hands