Slow PC

PC or app?

Check task manager -> cpu processes->memory->diskspace->startup 

Uninstall Old or Unused Programs and files
Update Your Software.
Upgrade Your Hard Drive -> SSD.
Upgrade Your RAM.
Check for Malware

Slow internet

Psychical connection, wifi
Speed test
Test Your Network on a Different Device.
Test different website or application
Ping, Traceroute the server
Check server logs, Cpu, Hardware, Memory, Processess

Troubleshoot link connectivity

check ticket history, any recent work on the link
check light indicators, device power
loopback test
vfl for fiber, continuitty test for copper
test with new cable, tranceiver
test port
check interface->errors->duplex mode->speed->routing