You can get power plug converters to allow for more SATA power plugs.
The boot files are probably on the old drive. You might attach a snipping tool picture of your disk management window for us to know for sure, but you probably have to make the partition containing the Win 7 install active..
Now you have two options:
Disconnect the old drive (or set the new one to primary in the bios). Use the install DVD to do a startup repair on the new drive. Boot to the Install DVD, and on the second window, select Repair. Go to Startup Repair and run it 2 or 3 times to make the new drive bootable.
Or, since you have already made the new partition active, you can add the boot files to it by using the following command. You will need to know the partition of the new Win 7 install and use that drive letter if not C:
Open an administrative command prompt and type the following.
bcdboot C:\Windows /s C:
Hit enter and allow it to complete. Close the window and shutdown. Disconnect the old drive, and you should be able to reboot into the new Win 7.
Rather doing all this, you might just use the SATA power adapter plug or set up a flash drive to boot and load Win 7 from that.
Operating System Win 7 x64
Computer Type Homebuilt
OS Service Pack 2
DirectX Version 11
CPU Type and Speed i7 3770K
Motherboard Chipset Asus P8Z77-V Pro
System Memory Type 16 GB Kingston
Video Card Type and Speed Nvidia GTX 680 (2)
Computer Monitor LG 27" (3)
Hard Drive Kingston 240 SSD
Optical Drives LG WH12LS30 Blu-
Modem-Router Type Linksys E3000
Network Adapter Intel Gigabit
Anti-virus Software MSE
Computer Skill Level Average Ability
Windows Experience Index 7.7