To see what system you have:
Start > Control Panel > System
That will give your computer model, the Operating System, which Chip you have and how much installed RAM.
When booting the computer you can get the "no signal" message until the computer starts to talk to the monitor. Usually it only stays on the screen for a moment, so the implication is that yours is taking longer than it should to boot up.
Start by emptying the recycle bin.
Have you defragged the system disc (C:) recently/at all? It's something worth doing regularly. Microsoft provide a defraggler but I prefer this one:
https://www.piriform.com/defraggler/download
Download it from Piriform and make sure you take the free option. You'll have to run the downloaded file to install it, then you can run it and defrag disc C.
If you would prefer to use the one provided by Microsoft:
Start > computer.
Then right-click Local Disc C: > properties > tools > defragment now.
It may take a long time, depending on the size of your hard disc.