Now finally seeing what system you have, it supports quad cores without bios lock :
https://support.hp.com/au-en/document/c01857670
I bought cpu:s from china and all have worked well, just have to be careful that seller has 99% good rating and some feedback on item is good aswell:
Under 50 euros you get what Coolness94 and i already suggested few times:
https://www.ebay.com/itm/Intel-Core-2-Quad-Q9650-3GHz-12M-1333-Quad-Core-LGA-775-Processor-Thermal-Paste/282644952232?epid=74093673&hash=item41cef3b4a8:g:-5wAAOSwKUhZs0OU
But theyre thermal paste i wont suggest, its always been trash
😀
Thermal pastes i suggest NT-H1 and GC gelid extreme, latter even slightly better. Use 80-90% isoprophyl alcohol to clean cpu, with wipes or qtips dipped into alcohol
EDIT: you need these thermal pastes only if you want to overclock your new cpu further, but also if you buy used Graphics card (since you need psu and Graphics card) and want to overclock these are nice paste for gpu chip too, went 10c lower after repasting with gc gelid extreme on my gtx 670