what causes these things?

[pkm]

Occasionally my pc will boot up without sound.

Some boots are also really slow.

These are only minor inconveniences but any tips appreciated.

And phenom x4 955 3.2ghz
On board sound (can't remember mobo)
8gb ddr3 ram
Hd xfx 6870

[shroudster]

driver issue likely

[vesseblah]

Yep, agree on driver problem. Extremely slow startup and shutdown times are 90% certainly caused by software problems, and other 10% by broken hardware refusing to load drivers properly.

If possible do clean install of Windows, that's the only way to make relatively sure software problems are cleared up and you only have potential hardware problems remaining.

[Twoddle]

Also run error checking on the hard disc, let it schedule on next reboot and fix all errors.