Lag while hold down a button/key

If I hold down the shift key, or almost any key for that matter it drops my fps from 60(v-sync) to around 30. If I combine holding a key down and pressing a button on my mouse it then goes from 30 down to 6 fps, but wont stay at that. It'll jump back up to 30 even when holding down the mouse button. Then when I release everything it jumps back to normal frames. I can hold down the mouse button with no fps drop, but if I spam a button on the mouse then it drops to about 30.

The mouse is a razor naga, and the keyboard is a $10 logitech or something cheap. Both are usb of course and I read plugging a ps/2 keyboard in would fix it but my board only has usb ports. There was also a mention of the keyboard ghosting, which I suspect is true because it's just a cheap one.

Not too big of a deal and will keep researching about the issue, but if someone that reads this knows the problem/fix right away then their help/elaboration on the issue would be much appreciated!

Edit: also tried typing "the quick brown fox jumps over the lazy dog" with both shifts held down and came up with: "HE QUIC BROWN OX UMP OVER HE Z OG". So yeah the keyboards a crappy one, but just wondering if buying a new/better anti-ghosting board would fix the problem.

I can deal with the mouse causing lag as I don't spam any mouse buttons and it doesn't lag when I hold down a mouse button. So as long as we fix the keyboard causing lag I'm happy.

Running 16gb ram, sandy bride i5 2550k cpu, gts 450 1gb gpu

A little outdated but should be able to run fine I can get a dxdiag also if you'd like.

Also, I just tried the same thing while playing league of legends just to test it out. It also lags when I hold down a keyboard key/ hit a mouse button. Other then that runs a smooth 60fps.

Another weird thing is I tried it out in skyrim and minecraft, and they didn't seem to have the fps drop at all when holding down a key/mouse button. Dunno if that's helpful at all.

It seemed to coincide with the keyboard repeat rate found in the control panel. If I turn it to as slow as possible and the delay as long as possible I don't get the fps drops from holding down the keyboard keys.

Though I still get a millisecond fps drop down to 30 and right back to 60. Really weird, but the games practically fully playable so if y'all don't know whats causing this issue then its no big deal cause I know you guys have way bigger problems to deal with. I'll keep researching the issue and post back if I find anything that solves it so in case someone else has the same issue.

I'll also run winMTR to see if there's any problems there also just in case. But yeah I'm with you, I've never heard of this problem before.

Ran the winMTR test and put the last instance server I connected to as the host and the highest average was 30 and the lowest being 19 so I think I'm fine on the latency side of things. I can send the actual results to you if you'd like.

Edit: Also forgot to put in that there was no dropped packets.

I have pretty much counter-acted the problem by turning off keystroke repeats completely using this guide: http://ask-leo.com/how_do_i_turn_off_keyboard_repeat.html instead of just slowing down the rate at which they repeated. Though when it was set to as slow as possible it didn't seem to lag either, so either way works.

The only problem is I can't hold down the backspace key to delete really fast or things like that, but I don't mind as long as the games playable now. Now this is just a workaround and like I said before it still lags for less than millisecond if I were to press a key. Of course that also means if I were to spam buttons then it would drop my fps down again but luckily my play style doesn't involve key mashing.