Your ssd's C: Drive only has 5.61GB of free space, that's 6% of free space. On a partition of this size you should have at least 15% free space.
Because you only have 4GB of RAM the swap space on this drive will wind up being used when you are running programs which are resource intensive. A swap file or swap space is a space on a hard disk used as a virtual memory extension of a computer's RAM. Having a swap file allows your computer's operating system to utilize the ssd to use its virtual memory to increase the amount of memory. This is a oversimplification, but you should get the idea.
Your Seagate has a great deal of space on its two partitions, I would transfer files and applications to this hdd to free up space on your ssd.
You need to test the rail voltages of your PSU. This can be done with the use of a multimeter with a DC Voltage scale. The following method will allow the PSU to run while bypassing the motherboard and other components. The case fan will run which will place a load on the PSU which will produce more accurate voltage readings than just reading from the PSU by itself.
The following procedure involves working with components inside the case and live voltages ranging from +3.3V to +12V. You need to follow the instructions carefully to avoid damage to the components inside the case and keep yourself safe.
The motherboard usually initiates the start or the PSU when the power button is pressed. This shorts the two wires from the power switch which send a signal to the PSU to start it. This signal travels back to the PSU via the green wire in the 24 wire connector.
Make sure the computer is turned off before going further. With the computer turned off disconnect the power cord from the PSU from the wall receptacle.
Open the side of the case. Important: Before touching any of the components inside the case you need to discharge any static electricity in your body by touch the metal of the inside of the case. It only takes as little as 10Volts to kill integrated circuits like the ones on your RAM modules, the human body can discharge amount of voltage in access of 2K Volts.
The PSU has a 24 pin connector which is attached to the motherboard, this needs to be removed from the motherboard. This connector has a clip on the front side of the connector which needs to be depressed to in order to disconnect the connector from the motherboard.
With the connector free you will need to place a jumper between the socket of the green wire (there's only the one in this bundle) and any black wire socket. A small piece of wire or a paper clip can be used for this, just make sure the jumper isn't touching anything else.
With the jumper in place it's time to turn the computer on. All you need to do is plug the power cord back into the receptacle, this will start the PSU.
With the PSU running you should have at least the case fan and the PSU fan running. When the power is on use a multimeter to read the +3.3V, +5V, and +12V rail voltages. You will want to set the meter to a 20V DC scale.
Readings should not have variances larger than +/- five percent.
If you are able to do this and have voltages within their normal ranges the PSU should be good.
To restore the computer to its operational condition unplug the power cord, remove the jumper from the 24 pin connector and reattach it to the motherboard. Plug the PSU back in and the computer can be started with the power button.