Hello and welcome to our forum.
Please know that, even if having multiple security solutions on your computer should mean that you are better protected, in fact these programs conflict, leading to computer instability and sometimes leaving you without protection.
Uninstall either Avast or BullGuard, according to your preference.
Furthermore, because you are using a Vista Computer and because the high usage is 50% not 100% and the affected process is SVCHOST, I strongly recommend you download and run System Update Readiness Tool for Windows Vista from Microsoft:
https://www.microsoft.com/en-us/download/details.aspx?id=1540 This tool will take a long time to run, but it's normal, so let it complete the job. After you run the tool and restart your computer, make sure you visit Windows Update, search and install all and any security updates. That should be the end of the problems.