I've had to deal with a infected PC before , the Virus Alert message popped up everywhere , it disabled , task manager ,hid the CD-ROM drive and C:drive .It's malware ,a fake virus , not strictly a virus . 2 programs you should always have on your machine ......MalwareBytes & SuperAntiSpyware . MalwareBytes is the only one you can install in safemode .It will leave remnants behind in the registry ,so use a registry cleaner .