What if my system is turned off and I want to turn it on from my college? It is not actually a good idea to keep my desktop on 24/7 ?
For most components that would die, like fans and hard drives, wear and tear really comes from starting and stopping. Components that can take damage from constant operation only do so if you always have them at their limit. If your computer is just idle most of the time then it is fine to run it 24/7 - you are more likely to run into issues with your operating system or programs becoming weird and requiring a restart than you are to be killing your computer.
You can look at your BIOS and see if it has a setting to automatically turn on at a certain time, but this might also mean setting your computer to auto-login depending on what type of remote access you choose to use. Another option is to try to set up Wake-on-LAN which means that the ethernet adaptor listens for a so-called “magic packet” and will turn on the system if it hears one. The primary issue with WoL is that the packet can only be sent on the local network unless you are able to get really fancy with the router (sending WoL over a VPN will work if it is a Layer 2 VPN, not if its a Layer 3 one. You can read more here https://hackernoon.com/wake-on-lan-through-the-internet-491817e2dd41 ) Alternatively some routers can send a WoL packet for you - the way you would use this is first you connect to your VPN server, then you access the router’s admin page, and from there you choose to send the WoL packet.