PC Getting Slow

[K3nny125]

Hello,my pc is fairly new, almost a year old now...so before the pc was running amazing...Ran games at 300fps and now the fps drops as low as 100. What do you think the issue is and please tell me if there is any solutions

Parts:
GTX 970
i5 4660 (or something like that)
G.Skill 8GB Ram
1TB HDD

 

[Harvey16]

State those parts.

 

[joex444]

I'm curious about your 300Hz monitor.