PC laggy and sluggish when connecting additional hard drives

Hey guys, weird problem here. The 2TB internal drive in my PC started slowly dying in December, and my brother got me an SSD for Christmas. I installed it, and it works amazing, flawlessly, and I love it. When I attempted to make my old dying drive a secondary hard drive, Windows recognized it fine (despite the SATA connection broken off) and I was able to salvage what I wanted from it. The speed of the transfer was blazing, and I was pretty happy, but I noticed Windows getting insanely laggy and sluggish.

The mouse would stop moving every few inches, and the keyboard would stop responding. Instead of normal lag, such as me typing this sentence, nothing happening, and then it appearing in full a few seconds later, when the lag would catch up...it would be a jumble of letters. For example, if I typed "wow my computer is going slow right now" it would come out "wom mpui gin sright n". That's a new type of lag for me, as my PC has never had issues. I assumed this was due to the death of the drive, and Windows having problems recognizing it or reading it. Sure enough, when I disconnected it, everything ran smoothly.

I have an iOmega 2TB external drive (LDHD-UP3 - don't judge, it was on sale) that I'm not too fond of but I use regularly for storage and backup. I usually have it plugged into the back of my PC, and this presents a whole other issue (which I need another thread for), but I've dealt with it fine and it normally works all right. However, I found out it's USB 3.0 compatible, and my PC has 2 3.0 outlets on the top, so I wanted to keep it plugged into there. But, when I do that, I experience that exact same type of lag as before, when the internal hard drive was plugged in. It's persistent and near-constant, but it stops the second I turn off the hard drive.

I've disabled antivirus, I've ran disckchecks, I've formatted...none of it makes a difference. Does anyone know what would be causing this with 2 separate hard drives connected in completely different ways? Any help would be greatly appreciated.
 
I don't know the answer but will comment about the issue of lag in typing. I have a wireless keyboard and mouse and I know when the batteries need replacing because the keyboard behaves exactly like yours and the mouse stops moving the cursor properly. Maybe your issue's connected with the power being drawn when you have the two drives connected. Don't rush out and upgrade your psu though. I only switch on my usb external hard drive for the occasions I need it. :)
 
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