Yes old HDD (SATA) can be reuse.

Intel Core i5 6400 - RM 815
ASRock B150M-HDV D4 - RM 399
GSKill NT 8GB DDR4 2133MHz Value RAM - RM 249
Palit GTX960 2GB GDDR5 Reference OC - RM 899
FSP Hexa+ 550W - RM 199
Bitfenix NOVA - RM 149
BenQ GW2255 - RM 439

Total: RM 3149 (Idealtech price inclusive of GST)

Intel Core i5 6500 - RM 885
ASRock B150M-HDV D4 - RM 399
GSKill NT 8GB DDR4 2133MHz Value RAM - RM 249
Palit GTX960 2GB GDDR5 Reference OC - RM 899
Samsung 650 Series 120GB SSD - RM 219
FSP Hexa+ 550W - RM 199
Bitfenix NOVA - RM 149
Dell S2415H IPS * - RM 849

Total: RM 3848 (Idealtech price inclusive of GST)

* Please note that S2415H is glossy screen type, you can see your reflection on screen if you are under bright light source, switch to something like Dell U2414H (RM 1065) for matte screen type, or just go with lower end 24 inch monitor like BenQ GL2460 (RM 539) but it is using TN panel. You can google for IPS vs TN for more info.

You can add another 1TB HDD (RM 219) if you think your old 500GB is not sufficient.