Screen no comprendo

Hi guys new here, so hopefully i don't annoy too many, basically im having this issue with the pc/screen, after a bit of playing not heavy games, such as fallout shelter or CSS. the screen will have vertical green lines or sometimes just a plain black screen. Im not savvy with pcs unfortunately, and am trying to learn, but this i can't seem to diagnose, I've run coretemp and other systems, nothing major found.Might be old hardware but computer savvy people told me it was okay, bu the issue could be GPU overheating and they couldn't find exactly what is was it either. Below is all the specs i think are necessary.Sorry for this.Below is the screen.Had to take the close shot so lines are visible. I have money to upgrade parts but unsure as to what or if it is worth upgrading if there is a bottleneck.
Phil






Name: AMD Phenom(tm) II X6 1090T Processor
Manufacturer: AMD
Speed: 3.2 GHz
Category: Extreme
Generation: 10th
Brand: Phenom II X6
Cores: 6
Name: AMD Radeon HD 7800 Series
Chipset: AMD Radeon HD 7800 Series
Manufacturer: ATI
Memory: 1024 MB
Video Card
AMD Radeon HD 7800 Series
Manufacturer
ATI
Chipset
AMD Radeon HD 7800 Series
Dedicated Memory
1.0 GB
Total Memory
4.0 GB
Pixel Shader Version
5.0
Vertex Shader Version
5.0
Hardware T & L
Yes
Vendor ID
1002
Device
6819
Plug and Play ID
VEN_1002&DEV_6819&SUBSYS_27331462&REV_00
Driver Version
21.19.519.2