My monitor has no signal

Hello, Recently i took my computer apart and cleaned it, when i put it back together, plugged the cables back in and turned it on everything seemed to work, the fans were working, etc. When I turned my monitor on it only said theres no signal. I tried all the tips i found on the internet such as reseting bios, checking with other monitors, taking out RAM but nothing works, other monitors and cables give the same results and none of the fixes i found online worked. My PC did this a couple of times before and everytime for some reason it would fix the next day but in this case i have tried everything and days later the monitor still says no signal. Please help!