Three possible causes:
1. A mains spike has caused offence to various bits of the innards.
2. A nasty virus has got in, and is doing nefarious things.
3. Something else.
For 1: Can you put things back as they were, desktop pic in place, that sort of thing? Does it stay put? Can you delete the offending new arrivals, and do they stay gone? If you can fix it, maybe just shrug and ignore it.
For 2: Do you have decent firewall and anti-virus software (refer separate thread, but something like ZoneAlarm ane AVG-Free)? If not, you may be in urgent need of help. Otherwise, ask AVG/etc to do a full system scan.
For 3: Tell us more about the symptoms.